One of the best arcade games, and the fact that it's only 400 msp makes it a must-buy.
I never really liked the multiplayer, but the single player is awesome. My friends and I used to try and best each others single player times while talking in party chat - better than the real multiplayer imo.
Firstly, they'll never release single player DLC. It's been too long and from what I've heard, it won't happen.
Secondly, a new one would be a lot better. It'd had all new levels and stuff so you'd get more enjoyment out of it. I really hope there is a new one at some time.
It's my goal to be quoted in someone elses sig.