We do a lot of griping about games which are all the color of dirt, slate, rust, mud, and ash. MadWorld does those games one better by having ONLY black and beige. It's instantaneously tiring. Maybe it's my withering old-man eyes, but I really did find it hard to make out the details of the scene. I realize this sounds like the ongoing Diablo 3 controversy, but can't we find some middle ground between "all-beige, all the time" and "rainbow unicorn puke"?
Colors aside, I actually think the scoring is what sucked the fun out of MadWorld. As Yahtzee pointed out, MadWorld assigns fixed points to certain moves, and there are a small number of moves that offer big points. The rest are a waste of time. This means that despite the freeform sandbox-esque nature of the arenas, you're really going to be grabbing dudes and killing them the same way over and over. The game even tells you what the big scoring moves are, so you don't even have any motivation to experiment. Since the announcers key off of what you're doing, it means they will repeat themselves over and over. The gameplay becomes repetitive and the announcers bombard you with the same three lines of dialog until you go mad.
All of this could be fixed if they had adopted a "Tony Hawk" style scoring system. All moves are worth full points the first time you do them, and diminish in value each time after that. This would encourage the player to use their imagination a bit.