Out of the GOG catalogue (as of May 2010) Lords of Magic is the only game I've played before. I know, sad, right? Anyway, this game was freakin' awesome back when I first played it in 2002. The perfect blend of turn based strategy and RPG elements blew my mind, and the mixture is still sweet to this day. The campaigns in the Legends of Urak mode are quite varied, and are all worth a shot. It's a highly strategic game with a high emphasis on leveling up your units, and if they ever did a remake, it would be awesome. That being said, the game hasn't aged too well. Not even the nostalgia can hide the clunkiness of the was-good-then-but-sucks-now controls. The battle music is kind of catchy, but it gets repetitive quickly, and the voice acting is downright horrible; you'll be happier turning the sound off and listening to your own music. Factions are mostly balanced, but there are some that are clearly better than others (Air freakin' sucks). The tutorials don't expain much, so you're better off just messing around on easy mode until you understand it all. If you're a fan of strategy and role playing games and you're looking for a great hybrid of the two, I'd say give Lords of Magic a go. Some of its flaws hold it back in the modern day, but I wish that developers would try to make more games like this. The premise is sound, but the execution falters a bit, so although this game isn't exactly a "timeless classic," it's still a good value at $5.99.
I'll admit, I never played Fallout until I downloaded it from this site. It's hard to believe this game came out when it did, it seems so ahead of its time. Most RPGs to this day don't come near the depth and complexity of Fallout. It's a ton of fun to play, and all the game's mechanics work extremely well. Buy this game, you won't regret it.