I don't really see how the game length would be a problem unless it's under 5 hours or so.
Which it wasn't, took me a good 15+ hours to 100% it which I believe is a good range for a game to have. Not so long that it gets boring, not too short that I'm aching for more.
Also I spent a few hours just replaying my favourite Modern Sonic courses for fun, just trying to get through as fast as possible because that's the greatest thing about sonic games; that sense of speed.
My single complaint would be the final boss, it's atrocious. *bleep* that thing, not even the music was good to salvage it.
Looking back on SA2:B, it was a really fun game but only when I played the sonic/shadow levels; the other characters were okay but it really slowed the game down. Chao Garden was a nice distraction and I loved it as a child but when I went back to it a year or so ago I found myself wondering what I enjoyed about it to begin with, it's still a nice distraction but I can't seem to praise it like other people can any more. I can't praise the game as a whole like other people can any more.