Attanck! is a fun shooter with a couple of neat twists that help set it apart from other games in the genre.
The first of which is the art style, with all the graphics being done in ascii and the action set against (or on top of) a ream of dot matrix printout paper.

The second twist lies in the control scheme. Each of the tank's treads being mapped to the relevant analog stick and controlled independently (a bit like a real tank I suspect). Push both sticks up and the tank will trundle forward, push just one and the tank will turn in the appropriate direction.
This seems a little tricky to begin with, but doesn't take long to adjust to and you'll soon be weaving your way around the levels with ease.

There's quite a few different enemy types to shoot, with newer ones being introduced as you progress through the game, and a larger enemy (sometimes more than one) to defeat at the end of each level.
You have two attacks at your disposal, a forward firing cannon and a mortar-style bomb. Both have infinite ammo and the game throws sufficiently varied combinations of enemies at you to warrant being adept at using them both.

Attanck! is a fairly short game, with only about 10 levels (if I remember correctly) to blast your way through. Once you've finished there's not much incentive for a replay, the three available difficulty levels not changing the game in any way other than by limiting the number of lives you have.
You are given a score at the end of the game based on how long you took over each level (there's a time limit) and how many enemies you killed, but a lack of leaderboards means you'll only be competing against yourself. However, despite these complaints, Attanck! is still worth the small cost, as it provides a limited but enjoyable experience.

Get Attanck on XBox 360