Winners and Losers after the Modern Banlist

The obvious questions

Q: Are Boros Energy and Amulet dead?
A: Not really.

Amulet has remained a tier-one deck. We all know the infamous copypasta, but the truth is that until Amulet of Vigor itself gets banned, and even then I would have some doubts, the deck will likely remain one of the strongest contenders in the format.
Personally, I’m happy about this ban. Lotus Field made the deck a bit too straightforward, creating situations where three lands, an untapper, and Scapeshift often translated into a lethal line that was extremely difficult to interact with.
Now the deck is less linear and requires more setup and planning to kill the opponent. That doesn't make it weak, though. It remains a powerful force in the metagame and is still capable of putting up excellent results.
A perfect example is Nathan Goldberg, one of the most accomplished Amulet pilots, who recently won an event with the updated version of the deck. His list featured Zuran Orb as part of the Analyst combo package.
Zuran Orb is a particularly clever inclusion because it can be found with Tolaria West, making it accessible during Scapeshift lines. It's a great example of how Amulet players continue to adapt and innovate, even after losing a key piece of the deck.
 

How about Boros? 

Well...
Phlage was certainly one of the best cards in the Boros shell, but I think its biggest impact was in slower, grindier matchups. Those games often revolved around Phlage itself, as most fair decks were also built around recurring value and attrition.
Losing that angle isn't a huge blow to Boros, though. The deck's strongest cards are still the absurd one-drops, Ocelot Pride and especially Guide of Souls. Those are the cards that enable the deck's most explosive starts and give it its identity.
It's no coincidence that Boros continues to overperform and put up strong results, winning Challenge after Challenge on MTGO. The real question isn't whether the deck is still good, it's how to build it correctly for the metagame.
That has always been a hot topic among Boros players. Different lists are often tuned to attack different metagames, and small card choices can dramatically change certain matchups.
With that in mind, here's the 75 cards I would register for the current metagame:

Arenas are much less necessary now that Phlage is gone, while Dalkovan Encampment continues to overperform. I also like having three basic lands in a format where land destruction is still a real consideration.
The three- and four-mana slots are a bit flexible, but the deck desperately wants sources of card advantage once the early game is over. Both Pyro and Roku do an excellent job of providing extra fuel and helping you keep up the pressure.
Roku, in particular, has become even better in the post-Phlage world. In Boros mirrors, you can now safely tap out for it without constantly worrying about dying to a hasty Phlage on the following turn.
The sideboard is built with my expected metagame in mind: Tron, creature-combo decks, Affinity, and various combo strategies. I'll go into more detail about those choices in the next section.

How about Cascade?

My first thought after the Violent Outburst unban is that Violent Outburst is just really annoying to play against, despite being relatively weak.
When Rhinos (and Living End, since it was the anti-Rhinos deck) was good, the metagame looked completely different. Yawgmoth and Murktide were two of the best decks, and Rhinos had access to Fury, various bounce spells, and four copies of Mystical Dispute. On top of that, the Rhino plan was often good enough to win games by itself.
Nowadays, the threats are radically different. An unchecked turn-one Ocelot Pride can easily outpace an Outburst, while the best deck, Affinity, has four Engineered Explosives plus Emry, alongside Kappa Cannoneer and Shadowspear. It also has countermagic and sometimes even maindeck Vexing Bauble. And that's not even mentioning Wrath of the Skies, which shows up in many sideboards.
The strength of the best Modern decks right now is that most, if not all, of their cards are powerful standalone threats, or they're very capable of killing you on turn three. Rhinos probably can't keep up with that. It can still steal games if the opponent is low on resources or has started cutting sideboard cards for the matchup, but I don't expect it to be a major player.
Living End is probably better, mostly because resolving a cascade spell often leads directly to a win, or at least leaves you with a much stronger board than two 4/4s. Even so, I don't see the deck performing particularly well when so many decks already play incidental hate, such as maindeck Thraben Charm or Tormod's Crypt, alongside sideboard cards like Vexing Bauble and countermagic.

As I've said before, the individual cards in Living End look like a pile of draft commons and uncommons, and they don't function particularly well unless you're cheating them into play. Even then, some decks, like Boros, can simply outpace your board with starts involving Guide of Souls and Ajani.

What’s the winner’s metagame?

Affinity is the easy answer. The deck plays what many people consider the best card in Modern, Mox Opal, and it is capable of producing unbeatable fast starts with Kappa Cannoneer while also playing slow, grindy games thanks to Emry and Urza's Saga.
It has strong board control through Weapons Manufacturing and Claws of Gix, as well as cards that fit multiple game plans, such as Arcbound Ravager. On top of that, it's not easy to hate out if the Affinity player knows how to play around the most common hate cards: Wrath of the Skies, Vexing Bauble, and Collector Ouphe.
I am genuinely surprised that Kappa Cannoneer is still legal in Modern, considering how miserable many of the games involving it tend to be, but that's just my opinion.
Another deck that is likely very good is Izzet Prowess. The deck was largely overshadowed by Boros because of Phlage, but despite that, it still managed a Pro Tour Top 8 in the hands of Justin Schabel. Now that the Phlage decks are gone, Prowess can fully capitalize on two of the best red cards ever printed: Cori-Steel Cutter and Slickshot Show-Off.
Prowess derives its strength from its ability to consistently threaten turn-three kills while also being capable of playing a longer, grindier game thanks to Expressive Iteration, Preordain, and the value generated by Dragon's Rage Channeler. Being blue also allows the deck to bring in countermagic after sideboarding, such as Spell Pierce and Spell Snare, giving it meaningful interaction against combo decks.
Goryo's Vengeance decks are likely good again as well, mostly because they have a powerful Psychic Frog + Quantum Riddler package in addition to their graveyard combo. The white splash also helps a lot when it comes to dealing with problematic permanents.
Moving away from the combo versions, I can also see Esper Frog + Riddler shells performing well, especially alongside cards like Overlord of the Balemurk and Phelia. Those decks were historically terrible against Boros because Boros could attack from so many different angles, but now they can keep pace simply by playing powerful standalone cards without having to rely heavily on the graveyard plan.
The final archetype that escaped the bans relatively unscathed is Eldrazi. Whether it's Tron, Ramp, or Broodscale variants, Eldrazi decks have historically had a terrible matchup against Amulet. While Amulet is now less popular—and significantly slower and more difficult to play—I could easily see Eldrazi making a comeback.
It's also worth noting that Eldrazi was heavily kept in check by Jeskai Blink lists that played multiple maindeck copies of Consign to Memory. I suspect that deck is either unplayable without Phlage or, at the very least, will stop playing Consign in the maindeck. The card was particularly effective because it could counter Primeval Titan's triggered ability, enabling some very powerful tempo swings.

Decks that I think will be good

Modern has, for the most part, always been a format of specialists. Right now, I feel the same way. If you have enough reps with your deck, you can probably tune it to beat the most popular decks by identifying which cards are actually good, which ones are traps, and by developing strong plans for the metagame.
I can easily see Merfolk, a deck that is notoriously weak by today's standards, picking up wins at a local FNM, just as I can see Yawgmoth, an otherwise solid deck with some notable weaknesses, performing well in a large open tournament if it is tuned properly.
Yawgmoth, and creature combo decks in general, are in a good spot right now because their main predators are gone. Grindy games involving Phlage repeatedly clearing the board and Amulet's turn three inevitable kills were some of the archetype's biggest challenges.
Creature combo decks also tend to interact well with other creature-based strategies, especially now that Orcish Bowmasters has become a staple for both defensive and offensive purposes. Access to Thoughtseize and other highly specific interaction pieces, such as Endurance and Force of Vigor, is often enough to keep pace with opposing combo decks.
On top of that, the deck's own combo is powerful enough to steal games out of nowhere, forcing opponents to constantly respect the possibility of an instant win.

UW Control might be in a good spot again, mostly because of its favorable matchup against cascade decks thanks to Orim's Chant and Teferi, as well as its ability to lock opponents out of the game with Isochron Scepter or Narset plus Days. The deck also benefits from having access to some of the best answers in the format, allowing it to adapt to a wide range of strategies while maintaining a strong late game.

There are many ways to build UW Control, and I expect players to experiment with different packages depending on how the metagame develops. Personally, I'm especially interested in trying a version featuring Flow State. After playing with the card throughout the entire Standard season, it has consistently felt very powerful, providing both card selection and flexibility. Modern is obviously a very different format, but I think the card has enough raw power that it deserves serious consideration, particularly in a deck that wants to hit its land drops, find specific answers, and reliably pull ahead in longer games.