If you're looking for a semi-entertaining game, go ahead and buy Joust.
The graphics are kind of grainy, and the sound is mediocre at best. The gameplay is very simple, but when gameplay is THIS simple, it becomes a game of luck and not a game of skill. Be ready for some frustrating experiences.
Overall, if you're a big fan of the original, go for it, but if you're not very familiar with, or fond of the series, it's really a waste of time.