Ahhh, it's kinda unfair because the Final Fantasy VII soundtrack is my hands down favorite. I could listen to the whole thing without skipping a track and enjoy all of them.
Taking that, and a lot of other great Final Fantasy music (Including Tactics, of course), and all those famous Nintendo numbers off the table: "Still Alive" from Mirror's Edge (I put it on a mix CD for a friend, and she said it was her "Life Song" for about a week), Time's Scar and Radical Dreamers from Chrono Cross, Jet Set Radio Future soundtrack, Silent Hill's main theme, Laura's Theme from Silent hill 2, the songs Melissa Williamson sings in Silent Hill 3 (Letter - From the Lost Days, You're Not Here, I Want Love (Studio Mix) ), Startropics soundtrack, Los Abysmos aka the music CHASM used for their trailer, "The Dawn Will Come" and a track titled "The Lost Temple" from Dragon Age: Inquisition and several of the bard's songs, "I Am the One (High & Dark Fantasy Versions)" from Dragon Age: Origins, I really enjoy the FTL title screen music, Halo Theme (Even though it's super cliche now), The Road of Trials from Journey, Baba Yetu from Civilization IV (Which, I realize is not exclusively from that, but...), Still Alive from Portal (But, who doesn't??), The whole Myst soundtrack (Though especially the Telescope theme and main Myst theme), Song of Mana from Legend of Mana, Small Two of Pieces and Star of Tears from Xenogears (Yeah they're sappy, so sue me!), Metal Gear Solid 2's main theme and "Snake Eater" from Metal Gear Solid 3, Tetris (You know the one), "The Venerable Forest" from Star Ocean The Second Story...... Geez, this long. Ummmm.... I'll just leave it there..... Wait, WAIT, "The Poet and The Muse" from Alan Wake. It's a great song AND a crucial plot element. More on that below.
I think that the most important aspect of a game tune is.... Being a fit with the setting. For example, I just recently (read, yesterday) was playing Fortune's Tavern and they have a classical soundtrack which is.... Nice? But it doesn't fit the setting the majority of the time. I mean, Super Hexagon has a better fitting soundtrack, and I would therefore say is a better game soundtrack. It may not be objectively better music, but it is a better set of game tunes.
And I would say that, like a movie soundtrack, most of the tracks are not entirely fair to judge out of context of the game. Some songs, Let's say "Eyes on Me" from Final Fantasy VIII for example, could easily be played out of context. However, the aforementioned "The Poet and The Muse" by The Old Gods of Asgard (A rock group IN the Alan Wake game world) is a nice story song on its own, but IN the context of the game it's amazing because it reveals sooo much about the plot and a crucial clue that the hero needs to complete his task, which I'm gonna go ahead and claim is something that hasn't been done before or since (Clues and important lore elements in conjunction)