Rolling and slope jumping are fun and important mechanics, but classicfags tend to reduce the entirety of classic Sonic gameplay to just those, when in reality in actual classic Sonic level design they are not as prominent as they are made out to be. Sonic Utopia might be fun, and I think it's a cool experiment on its own, but people try to say it's the true realization of classic Sonic gameplay in 3D and it really isn't. The classics had a lot more mechanics, including many that have nothing to do with rolling or gaining speed, and also made use of other aspects of the physics. And of course they had actual objectives, level design, shortcuts, gimmicks, time, score, special stages, and more.
SRB2 didn't have slopes at all until a few years ago, and I think that worked in its favor. They were able to focus on other aspects of the game and level design, and now that it finally has some occasional slopes it's even better and it feels more like the classics than anything that's come out of the obsession with rolling physics and slopes (which can still be fun, mind you). Of course SRB2 still has its own mechanics that distinguish it from the classics, especially the thok, and it's still missing the loops which are an iconic visual element of the series. But in terms of the core gameplay I think it's the closest to translating the classics to 3D. I think SA1 is second place