While Dune 2 was great, check out fan-made Dune 2 eXtended - you can play as the Fremen, Mercenaries, or the Sardaukar - and it's a good bit more challenging. I've tried running it on a 16 MHz 386 and after the third level it gets unplayably slow. Probably you'll need at least 25 or even 33 MHz 386. Plays fine on a 486 DX2/66.
