Hmm... Not in any order:

Halo (1, since most of the good ones from 2 and 3 feel like building on 1s moves, or remixes.)

TES soundtracks, Morrowind's noncombat in particular, Skyrim's combat.

Crusader Kings (Ok, I'll admit, it just has Sabaton songs in it)

Zelda - more or less every game has at least one catchy melody, usually more. This is something lacking in the genericized Rock n Roll/Dramatic Orchestra of most other games these games. They may have good songs, but I can whistle Zelda years (& decades) later.

Mechanicus, to quote Mandalore, "Other electronic songs have a bass drop, this has a pipe organ." Praise the Omnissiah.

Sunless Seas - You're far out of your depth in the depths, gods and devils fear to tread, but you're the captain and this is your sea. THESUNTHESUNTHESUN

Dark Souls - Ash Lake. Just that one song, and only in game, since the OST doesn't include the quiet rising as you round the bend of climbing down that miserable tree and come out into a strange wonder.