Earth Invaders 0 is an old school side scrolling 2.5D game, developped by smealrum(code) and lobo (GFX). Why 2.5D ? Because, as you may notice, the game features a classic 2D gameplay with a 2D background, but every single element, item, character of the game is actually real time rendered in 3D.
Enough of technical stuff. EI 0 is not only a side scrolling platform game but also an infiltration/shooting game which takes advantage of the unique features of the DS, such as the touch screen.