Story mode takes a while to complete / to see the True Ending. Sequel is out in two and a half weeks, and it is also $37 on Amazon (with more deals to follow probably). While I recommend the series, especially if you're looking for a fighting game, holding off until the follow-up is the better cheapass decision.
Only get if you're a completionist or if you have no intention of getting the sequel til the price drops. Enough has changed that you'll have to relearn combos, and the original will probably hardly be played online. Story mode is posted all over the web anyway.