Following some of your suggestions, I listened to Final Fantasy music by Nobuo Uematsu and I really enjoyed it. Especially FF3 (I couldn't believe it ran on snes) and FF7 (cd quality music holding midi references). Did not like FF8's and FF13's. FF11's surprisingly had some folk-like notes, which was also good. Twilight Princess' sounded similar. Now none of them sounded really like a game soundtrack to me, and I see two possible causes:
1) place of origin: while most games I played were western-made, those were totally eastern
2) platform: I have never really accepted anything other than a PC, and the FF culture is a console one.
Anyhow, listening to these soundtracks made me regret never playing the FFs (tried with ff7 once, but the version lent to me proved damaged).
Megaman 2's soundtrack was also great, as was Dark Forces' - a good listen, even though youtube could not present the music's dependance on player action, so I just took your word on that.
Now I would like to remind myself and everyone else, that many great games did not have great soundtracks, so it's not mandatory to have one. Some examples (the example part may be boring, but if you know any of these games, then you might know what I'm talking about - it's a chance I won't miss):
UFOs (more on them here)
Civilization 3 (and also 2, unless my memory is pulling a prank on me)
Fallouts (1 and 2, Tactics wasn't such a great game according to me and I don't know about the 3D ones' music)
Half Life (part 1, skipped the 2) and CS
Heroes 4 (not a great game, but a good one, despite poor music and annoying graphics)
Morrowind (also good, but not great; mentioned because the music technically good, yet still annoying or soulless)
Minecraft could belong here too, couldn't it?
Of those games, which music was good, some was good for listening, and some mostly as a mood creator for the game. Some examples of the latter:
Dungeon Keeper (for the most part)
Panzer General 2 (as above)
Warlords 2 (described here)
Warcrafts 1 and 3
Medieval: TW (part 1)
Prince of Persia (the original one; separate post here)
Jedi Outcast and Jedi Academy... basically all star wars games I played (because it was not original)
Pirates Gold (some sea shanties that were great for the game and I loved listening to them; normally I dislike shanties)
Samurai Shodown 2
Now some winners (music both fitting into the game and great for listening):
I already mentioned Betrayal at Krondor (in my previous post) and HoMM2 (one post before that)
Unreal Tournament (the original one, from 1999)
Privateer (definitely deserves a separate post, but hasn't yet)
Civ 4 had a great selection
Of course these are all just opinions based on my experience, and I'm certain I forgot some cases worth mentioning.