The game goes for retro with 2D spritelike graphics ranging from Atari 2600 to 8-bit Nintendo in quality for the deliberately pixelated games. The more realistic ones use photo cutouts and a mix of other styles, which changes things up fairly well from game to game. The whole soundtrack has a deliberately retrogaming vibe to it--it's a bit more technologically advanced than something an actual Atari 2600 could conjure up, but it's got that kind of sound.
Hot Pixel has its moments, but it's shamelessly derivative of Nintendo's WarioWare games, and loses out a bit because of its lack of originality. At the same time, it's also a fairly good clone of the WarioWare concepts, so if you're a PSP owner wondering what all the fuss was about, you'll probably have an OK time with Atari's version.