MDK was a whole barrel of laughs. The comic enemies, the pure adrenaline rush of the combat sequences, and yet the great balance with the puzzles, that although sometimes stumping you, never quite perplexed to the point of frustration, and the truly awesome, and well animated (for the time) character of Kurt Hectic.
MDK 2 still has many of these elements, and does add some extra bits, Max's levels are pretty cool, any game that allows the player to wield four chainguns simulataneously is doing something right, and the Doctor's levels, though often frustrating do help to break up the game a little bit.
That said, when I say the Doctor's levels are frustrating, I really mean it. The control system for his inventory is un-intuitive, which is not too handy in the middle of a boss fight (A point and click system would have worked much better in my opinion) and although he is not suited to be an action character, there is still an insistence on putting platforming sequences which sometimes require near pixel-perfect accuracy to beat. Every time one of his levels came up, I found it a chore, and found myself wishing for one of Kurt or Max's levels.
The other thing that annoyed me slightly was the voice acting. There is a very fine line between good and bad comic-book style melodrama, and though the team definitely tried to pull the stops out, something about the gags just fall flat, time after time.
However, all that said, I must re-emphasise that there is some great high-adrenaline fun to be had in this game, particularly in the combat, and Max's jetpack sequences. Also, the addition of mouse aiming is a welcome adjustment, and seeing as it's only $5.99, (or in my currency, £3) it may be worth a look in.