Best ingame soundtrack?

Runescape - Stealing creations <3

Halo Combat Evolved. Especially the main theme.

Railroad tycoon 2

Kameo

Tropico

BF Vietnam

Space Channel 5

Caster

Impossible creatures
to name a few

EDIT:

gotta add Jazz the Jackrabbit

Transistor & Bastion
To the Moon & A Bird Story
Hotline 1 & 2
Super Hexagon

Frozen Synapse. Hands down winner for me.

NMRiH

I'm not sure if I like the Beatmania soundtrack more or the SDVX soundtrack more but leaning towards Beatmania.

Skyrim!

Morrowind

Well if we don't go deep in history I would select Alan Wake. Best modern game soundtrack, great neoclassic/ambient orchestral score by Petri Alanko, a bunch of great songs in-game, a bunch of great songs in episode ends, even some special songs from Poets Of The Fall.

Hotline Miami 1 & 2, The Binding of Isaac, Super Meat Boy, Skyrim are the first ones coming to mind.