If you mean you played Steams Sonic Adventure vanilla, then I've encountered a few physics issues as well as a sort of "feeling" it doesn't play like the original. I just can't play sonic Adventure without BetterSADX now.
Well, that was not surprising.
Once we taste the better one, it's hard to go back to the "not" better one;
For example, playing Sonic 1 in original Mega Drive now feels lacking since there is no spin dash yet.