I thought this would an interesting thread as I am a huge music lover and video game soundtracks provide some of my favorite music.
1. Banjo Kazooie - This game pretty much started it all for my love of video game music, it's genius. Walking around Gruntilda's Lair with that overworld song is a treat to hear and it fits the mood perfectly. Freezeezy Peak is nice as it does give a fast feel to the map but still "chilled" out. Grant Kirkhope became big just off of that soundtrack and rightfully so.
2. Spyro the Dragon (pretty much the first 3 games since they are all amazing) - Look I think it's safe to say that the soundtrack was bound to be good with Steve Copeland making it and my god is it ever. I can't recall everything because there are a lot of levels and a lot of music but one thing I can note is the drum work (composer is a drummer of course) and and the ringing bells added in perfectly at the right time.
3. Dustforce - I've never even played this game but I stumbled along the soundtrack one day it has a certain heavenly sound, I often listen to it while playing other games. It's in the chillstep category but unlike other chillstep it works better when playing games because it keeps a certain video game-esque sound to it.
4. Skyrim - Now I'm sure many of you are saying a lot of it is recycled from previous Elder Scrolls games but overall I prefer the music Skyrim has to the others. I had a teacher who actually played this music in his classroom. The horn that's often used in the songs gives you the feel of an adventure and I love adventure.
5. Majora's Mask - Another game I've never played but hands down has the best music a Zelda game has ever had. I really want to play it so I can feel the music and the mood it sets while playing but to be fair, the music already does a damn good job of it without playing the game.