While it's not a pixel perfect copy, the graphics are very close to the original and the blocky, pixelated visuals give the game a distinct retro feel. My only complaint is with the keyboard handling. It seems to rely on the keyboard repeating the keydown events when you hold the key down. This means there's a small delay from when you press the key until your cannon starts moving.

All in all, this is a great Space Invaders clone, even if it lacks a few minor details in order to be complete. Also check out his blog post about the game