I think it's the best 2d fighter. I realize it's completely subjective, but even judged technically, it holds up.
The sprite animations are very fluid and well designed. The roster was diverse. Tons of characters without descending into "Evil Ryu" silliness.
The combat was balanced. Ex-moves were introduced which added another layer to your moves that felt natural to play. It had the parry system which I thought was genius as it can nullify chip damage and made turtle strategies disadvantageous.
As an SF fan, it was also notable because it progressed the story in a natural way. Returning characters were older. Most of the roster were new characters, many of them with connections to the old characters. The music and visuals and play, it all comes across as a very mature street fighter game. It's like it expected that the original players of the SF series have themselves grown up and this is the fighter they would want.
What I'm saying here applies to all SF3 versions (New Generation, 2nd Impact, and 3rd Strike). 3rd Strike was their final version of the game with the final balancing and additional characters, movesets, etc.
SF4 just undid all that pretty much. Such a disappointment. They pretty much went the SF:EX route. Same original roster and movesets. Same 3D visuals as the gimmick. Same ridiculously designed new characters (Remember D.Dark?).
Honestly, if you don't like Street Fighter, but are willing to give it's best game a shot, check out Street Fighter 3.