Simple and awesome.
Gameplay is action-packed and fun, dodging rockets and lasers and guns, but can get frustrating when there's a level that you just CAN'T beat. Luckily, the levels are not in a straight line, rather, there are 10 columns of episodes that when you play the one at the top, it unlocks the next one, meaning you always have access to 10 different episodes. I'll give N a 9/10, because sometimes it's a bit too frustrating.
Graphics are simplistic, but they work well. Enemies and obstacles are all easy to tell apart; it's hard to confuse them. Also, the physics engine makes death fun to watch.
Sounds are also very simple -- there is no music, just plain sounds for lasers, picking up gold, splattering against the ground, and some other things.
It has 100 episodes of 5 levels each; that's 500 levels. Some are very simple, some are very difficult -- 500 levels in a FREE game can be nothing but 10/10 for value. Also, N has a website full of maps that other users have made. (you can make your own maps too) That's alot of maps.
Yeah. N's awesome. Play it. But don't play the online version, because it only has the first 30 episodes instead of the full 100!