Nasty is an excellent shoot-em-up platformer that's part Bubble Bobble and part Contra.
The similarities to Bubble Bobble can be found in the level design and the game mechanics. Each level comprises a single room that must be cleared of enemies before you can progress to the next. If you drop off the bottom of the room, you re-appear at the top, with the same rule applying to side-to-side movement.
There's a time limit to each room and, should you fail to kill all the bad guys before it runs out, an indestructible evil creature will appear and chase you around the level until either it kills you or you finish off the remaining enemies. You deal with enemies by shooting them, and you can fire in any direction, which is where the Contra influence is noticeable.

There are 100 levels in total, with each one presenting a different challenge. The layouts are varied, providing fresh platforming, and new enemy types appear as you progress through the game (including some bosses).
There are also pickups to collect that boost things like your speed, jump, weapon damage and fire rate, as well as varying shot patterns and giving you temporary bonuses like a time freeze and invulnerability.

The game can be played solo or with a friend in 2 player co-op. There's also a 4 player Battle Mode available (which I personally haven't had the chance to test out).

Nasty is a highly enjoyable game. The main challenge lies in getting through all 100 levels, but with the ability to use continues, an auto-save every 10 levels, and a generous amount of extra lives being awarded, means that it doesn't get frustrating at any time.
The controls are well implemented, the level designs interesting, and the graphics are simple yet clear and colourful.
The sheer amount of content packed into the game makes Nasty an absolute bargain at such a low price, and I'd thoroughly recommend it to anyone.

Get Nasty on XBox 360