Atmosphere/Indie (Not usually a fan of the cheap and nasty stuff indie devs throw in, but these ones are a nice blend of retro and modern):
- FEZ
- Minecraft
Battle Mood (Music to get your heart pumping; some of the licensed games below also have some really solid battle tracks too):
- DOOM
- Call of Duty (Modern Warfare 1 & 2)
- Ratchet & Clank 3: Up Your Arsenal
- Portal 2
- Star Wars (KotOR, Battlefront, Force Unleashed)
Cinematic Mood (If you want more of that Halo feeling, this is the category you want to focus on):
- Assassin's Creed (2, Brotherhood, Revelations, 3, 4: Black Flag)
- BEYOND: Two Souls
- Destiny (1, Rise of Iron, 2)
- Far Cry 3
- Halo (2, 3, ODST, Reach, 4: Deluxe)
- Mass Effect (1, 2, 3)
- Mirror's Edge
- The Last of Us
Comedic (Light and playful, for when you need a laugh):
- Psychonauts
- Sam & Max
Licensed Tracks (As well as good composed scores, these all have amazing selections of licensed music):
- Grand Theft Auto (Everything between 3 and V)
- Life is Strange
- Need for Speed (Underground (1 + 2), Undercover, Most Wanted (2005), Hot Pursuit (2 + 2010))
- Saint's Row: The Third
- Sunset Overdrive
- Tales from the Borderlands
- Telltale's Guardians of the Galaxy
Others (Some games have a couple stand-out tracks, I'll let you explore for yourself here)
- APB: Reloaded
- Batman: Arkham Knight
- Bioshock (1 & Infinite)
- Borderlands 2
- Deus Ex (GotY Edition, Human Revolution)
- Doom (1 & 2)
- L.A. Noire
And yes, I heavily dislike the Undertale soundtrack. I'm just waiting on some scrubs to post some Japanese or retro stuff that already irritates me how anybody could find that decent.