I can't really comment on the physics until I've played it myself, so as of now it's the visuals and animations that I think I can have a more reliable opinion on. Running itself looks quite good, though I can't say I've ever been a fan of the mid-air running. It always looked too wacky for me. As for the little touches, while some of them are nice, I'd rather see a "less is more" mentality when it comes to Sonic game graphics. You can make an insanely complicated level (see much of Sonic CD and Sonic 4's Mad Gear), but you also gotta know when to stop in terms of sparkles, flares, shines, glows and dust on items and characters. This video, for example, goes overboard on the ring sparkle and running dust cloud (even trumping Sonic 4's dust clouds). Looks good for a minute, but imagine a whole game with crazy sparkles, trails of brown dust and badnik parts flying at you.
In the end, if this game's goal is to remake Sonic 2, why don't I just play the Sonic 2 created by SEGA?
I wouldn't say we've been "praising" Sonic 4, check my review and George's review. Those in the positive here find it to be an enjoyable game that has room to improve in subsequent episodes, hence the B rating. Were episode 2 to improve the physics to most of the detractors likings (I'd ignore the flat out crazies though), introduce original environments and add Tails to both episodes, Sonic 4 could very well become an "A" in my opinion.