How about a 2 player centipede game similar to the 2 player joust pinball. (edge to edge).
The trick is this. When you shoot the centipede, it will split it in two like normal, but going the opposite direction.
So each player has a side. And the centipede starts in the middle (maybe two of them, one in each direction).
Then add some fun. If you get shot by the other player, you get stunned for a second.
that would be fun.
BTW, I started a Mr Driller clone in java (to get on my phone... I love mr driller). It was going to use DigDug graphics since thats not my strong suite. I got to the point of having a guy moving down, and the blocks dropping, but not scrolling or have air or anything.
making a game where it uses the graphics of others takes a lot out of the design of the game. MUCH easier if you ask me.
A 2 player DOT would be cool, but I'm not sure how many people could play it well. Heck a two player centipede would be the same.
I would love to see more 2 player robotron games... but we have total carnage and smash tv. But they are so damn fun.