The graphics are pretty good in Monsters vs. Aliens. The characters look very much like their movie counterparts. They are cartoonish in appearance, but that's to be expected since the game is based off of an animated feature. The various areas each have their own unique feel, so you don't get the feeling that you're just playing the same thing over and over again. There's not a huge variety of monsters, but that's because they are mimicking the movie monsters.
The background music is upbeat and keeps you going. Granted, you really don't need to keep the volume up, but I would recommend it since you do get actual voices with the text that you can read. I really like having people actually talk out loud, especially on a DS game. It's something that is just usually missing from DS games that I really do miss. Not only do you get the voices in the cut scenes, but you also get them during the areas. The characters make little comments or grunts based on what you're doing. It's those little things that just make a game more entertaining.