This is a shameless copy of Worms 3d and Worms 4 compiled into one game that somehow manages to be worse than either of them seperately.
They haven't balanced a single thing, not even the scandalously overpowered weapons. Searching for a multiplayer game will dim your screen permanently, you will have to restard. The netcode is just as bad as it used to be. There's a lot of paid DLC and promo items you get for buying specific other games. The menu screen is also worse than both of the old games.
Worms 3d and Worms 4 Mayhem were PS2/Xbox games. Worms Ultimate Mayhem is a repackaging for the PS3 and Xbox360. There is absolutely no point in buying this if you play on a computer. The PC optimisation is poor at best, and still non-existant for Linux and OSX.
Whoever was marketing this game either had no idea what they were doing, no contact with the people making the game or lied through their teeth all the way to the bank. Whatever the case, they have definitely never played worms in their entire life.
My advice: go and seperately buy the original 2 games in a bargains corner. Do not support this kind of repackaging.