I'm really impressed by what has been shown. I was somewhat lukewarm on Streets of Rage 4 until now, but I'm very interested now.
The graphics style does look a little Flash-like, but the color saturation and art design looks very good. The streets look suitably dark and sleazy. You might complain about the lack of "pixels," but that's what happens when you render everything in 1080p. If you want that classic look, you'll have to go back to 240/480. The animation looks wonderfully fluid and definitely looks like a "next generation" sequel to the Genesis classics. I'm glad the developers didn't use 3D polygons. Keep it 2D and hand-drawn.
The gameplay offers up some new changes which is very welcome, such as air juggles. I do hope there are some new villains to face instead of just punching out the same group of bad guys all over again, but like the wardrobes, I suspect that fans would cry foul if anything were really changed. I also hope the developers remember how Sega broke up the action in Bare Knuckle 3/SoR3 with scenes like the bulldozers and the bombs. Don't just give us endless waves of fighting, which becomes repetitious and boring very quickly. Pay careful attention to how SoR2 varied its environments and battles from scene to scene, and generally kept those scenes short.
As for the other characters, I expect all of them to be playable, either at the beginning or as a post-game bonus. I don't know if SoR4 will feature more than two players at once, but I really wish we get 4P action. Please give Max a bunch of new wrestling moves. He needed at least one killer throw to rival Mike Haggar. I suggest stealing a couple throws from Virtua Fighter's Wolf and Jeffry.
Oh, and they're getting Yuzo Koshiro, right? Maybe they should go for a different sound than early '90s techno-pop this time. Again, fans would throw a fit if anything changed (they threw a tantrum over BK/SoR3), so I'd expect the sound composers to party like it's 1989.
Overall, everything looks great so far. As always, gameplay is everything and that's where SoR4 lives or dies.