If you're a fan of the Street Fighter franchise it is mandatory for you to pick this one up. At this point it might be better to purchase Super Street Fighter IV as it offers a bigger rooster. Also, Ultra Street Fighter IV is scheduled to be released this year around the summertime.
There are not many old-school fighter games on PC these days. You have the remade Mortal Kombat, too, so there isn't really anything else out there for us PC gamers. Just make sure you have a controller as with the keyboard it is a pain in the ♥♥♥♥ to play the game.
Interestingly, the story takes place right after Street Fighter II ended. Chronologically, the game can be put between the 2nd and 3rd episode. Bison's Shadaloo organisation still exists and organises another tournament to gather the best fighters in the world - this time, however, instead of Bison you have Seth as the final boss. Seth combines the best moves of all the players out there - he has a lot of counter special attacks, very agile and overall a pain on harder difficulty settings.
Gradually, you can learn to fight with each SF character and can continue to play online. You need a lot of time and effort to master these fighters. You can unlock many more as you progress through the game.
Overall, this is a really good game. When I was young my parents bought me Street Fighter II for the Super NES so for me this game was instantly captivating.