The ancient greats, I would consider to be these:
Final Fight
Streets of Rage 1 and 2 (yes, I like both about equally)
Knights of the Round (ideally SNES because of the control rework)
Double Dragon (NES)
Vendetta/Crime Fighters 2
There are a few old beat em ups with strong reputations that I haven't gotten around to yet. Those being mainly Violence Fight and Undercover Cops. I mention them so nobody thinks I believe the games are bad. I just haven't played them at this time.
When it comes to modern games which are awesome, and show a depth and intentionality of design similar to the old beltscrollers, I'd nominate these:
Fight 'n' Rage, as mentioned. Fight and Rage is a difficult but supremely fair game, with impossibly deep combat mechanics. It's clearly made by someone who understands what brawlers are capable of and knows that they are FAR from a mindless genre. The fact part of the difficulty increase manages game speed, and that turning this up doesn't snap game balance in half, really shows how well he thought through his design. The faster the game gets, the faster and better YOU get, and yet the game continues to work as intended.
Double Dragon 4. I don't know why I like Double Dragon 4 so much. It clearly reuses a lot of assets from the nes games, almost to a fault. Levels are sort of bland in appearance and a lot of mainstream reviewers slagged the game off as repetitive, boring, standard brawler complaints really. But it's surprisingly good! There are only two bullshitty platforming segments in the run, which is solid as hell by FC DD standards.
The game is also a really nice length. A lot of modern brawlers are way too fucking long. DD4 is a 20-30 minute 1cc. Very manageable for repeat plays. Additionally, the game has extras out the ass, mostly in the form of extra characters. Almost every character in DD4 is playable in the main story mode. If you wanted to go through as Abobo, you can. Prefer Burnov? He's there too. Every boss and enemy is playable. I think the game gets more fun the more you play, because of all the extra characters. They're not particularly balanced, but that's also in service to fun. It's just enjoyable to kick back and stomp faces with an overpowered Abobo, and those hellish platforming segments (there are only two) serve to balance some of the overpowered characters. The stronger a character is in combat, the less good they tend to be in the platforming. Which tightens up the window of error on those platforming segments. Surprisingly clever design.Just keep in mind that DD4 kind of looks like garbage at first blush. The visuals are very underwhelming. You have to dig in and play around to see how fun it is.
Streets of Rage 4 is a cool game, but it has some things I didn't care for. A lot of beat em ups made nowadays tend to be too long, and I also feel they abuse enemy and player i-frames way too much. SoR 4 is usually fine on this front until the bosses come out. Then it gets a little obnoxious. Old beat em ups abused i-frames too, but generally the "classic" ones were somewhat smart about how they did it. If not, then the game as a whole was so influential that such flaws could be overlooked. I like SoR4 and Adam is my favorite beat em up character to play as (in any game), but the karate guys and some of the bosses are shitty.
Okinawa Rush is very cool, but I haven't played it enough yet. I mention it because I think OR deserves a closer look by those who really love and understand beat em ups. It could potentially have as much depth as Fight 'n' Rage, but the community isn't there for the game.
Was a good one, that. 
Turrican is an esteemed Shumps Homie, I'm sure he'll be back after inadvertently sparking The Great MD/SFC Dogpilling Of 2021. 3;
