Final Fantasy IX, which is also my favourite game of all time, the story, the characters, the music, the gameplay, everything about it is just perfect.
Morrowind also comes to mind, I have seen a lot of flak towards vanilla Morrowind, but I think the base game with the expansions is just incredible, I find that most mods I tried using didn't work properly, bugged my game or just marred the experience.
Fallout New Vegas, I played the base game for upwards of 200 hours, I have yet to play it with mods, but if I can add a bunch of choice mods, fix the bugs, fix the performance and crashes, then I could play that game forever and not get bored, there is just something about the Mojave that keeps me coming back for more.
Shin Megami Tensei IV, with fast combat, bitchin' music, a world oozing in atmosphere and the excellent demon fusion system, its an absolute gem, its also an anti-grind, while you will fight a lot, you never really have to truly level grind, if you keep your demons up to date via fusion and update your equipment now and then, you will progress comfortably the whole way through.
Final Fantasy XII, yeah I know, the game that is second only to FFXIII in absolute scorn from many an FF fan, say what you want, the game had a ton of different ways to mix up the combat, the excellent gambit system gave you complete control over your parties actions which opened up tons of strategies. You also had a shit ton to do, with hunts, treasures and other such things just waiting for you, the game rewarded you heavily for going off the beaten path (and sometimes punished you, freaking Zallara)
