I think people seriously overstate peoples dissapointment with the last 3 Sonic games.
Sonic Adventure was the first to try it, and people loved the Sonic & Tails levels. People wern't too happy with Amy, Big, Gamma or Knuckles' stages, but they were still fun [and only needed to be finished once anyhow]. The story was very good considering the other stories for platformers at the time, unfortunately the cutscenes were incredibly flawed.
Sonic Adventure 2 had some fantastic Sonic / Shadow levels. The last level is just absolutely crazy and needs your best reaction skills if you intend to beat it. To get an A in that is something you must master. Failing is almost always your fault, not the game. The Tails / Knuckles levels were extentions of Gamma and Knuckles' levels in SA1, but people got a bit sick of them, wanting a normal Sonic game. The music was IMO a bit up and down. I like the Butt Rock of Sonic and Shadows House music, but wasn't too much of a fan of Knuckles / Tails' music. Eggmans was good too.
Sonic Heroes basically gave you a simple 'Sonic game' with a twist, you could use different character abilities. if you're any good at the game, you can play the game with no problems. People gave up too easily on this game IMO. It gave you the fantasy levels people had been asking for, LONG levels [between 5-10 minutes long], as well as an upgrading system, and 5 different versions of each stage, all which you had to memorise. The music was great for the most part, a few [Like the Jungle Levels] were dissapointing, but Casino Park and Bingo Highway's music nice. If you played the PS2 version, I pity you. It's an absolute SHOCKER of a game. Play the Gamecube version, it's 100x better.
Now here we have a game where we've got about 1:30 of footage, with horrible artifacting in both versions of the videos, and looks very similar to Sonic / Shadows levels in Sonic Adventure 2. You know, the GOOD ONES? In fact, the whole gun thing looks entirely optional in use, I'm sure that a batting on the head will do just the same thing it always did. It looks exactly like e-123 Omega's "Jump + Action" command in Heroes.
Until we know more, just wait :|