Wishbone: I'll definitely recommend both Sacrifice and Giants: Citizen Kabuto. They are two of the most underrated gems of all time. I love the first MDK too, although the controls are hard to get used to nowadays. I never could get into MDK2.
Sacrifice is a unique game. It's a 3rd person RTS, in which you control a wizard who battles by summoning creatures and casting spells. The graphical style is innovative, and the voice acting is phenomenal (especially Tim Curry as Stratos).
Giants: Citizen Kabuto is the only game ever to bring me close to physically vomiting from laughing too hard. The humor in the game is over the top, very quirky and quite frankly hilarious. The game itself is a hybrid like Sacrifice, combining game mechanics from different genres. It's basically a shooter, incorporating elements of squad control, base building, racing and other things.
Giants was actually made by a company formed of people who left Shiny Entertainment. They knew about Sacrifice, and they wanted to make something to compete with it.