loxy said:
In-game music? Don't you just mean game music?
Either way, my answer would be Elemental Gearbolt or REZ.
Awesome choice there! I'm shocked that someone else even thought of Elemental Gearbolt. The soundtrack is absolutely amazing, especially when you consider that it is simply a lightgun shooter...
Moving onward with more obscure music...
That also brings to mind Soukaigi's original soundtrack. The game itself simply wasn't very good, but the music was so incredibly original and inspiring that it made you want to play. The entire soundtrack was recorded with real instruments and I believe it was composed by Hiroki Kikuta of Seiken Densetsu 2 & 3 fame (though Soukaigi destroys them both).
Then you have Baroque for Sega Saturn. I believe it was developed by STING, who handled Treasure Hunter G and (shudder) Evolution 1 and 2. The game was quite dark and atmospheric, but it was the music that really set the stage. Beautifully haunting tunes that almost come off as a combination of Final Fantasy Tactics combined with Silent Hill. This soundtrack was created and composed by Masaharu Iwata.
On a COMPLETELY different note, how could one forget the crazy catchy tunes of Crusader No Remorse? They were tracked MOD files, I believe, but damn did they fit the action. The very first mission takes quite some time to complete, yet that opening song never grows old.
Perhaps even stranger; Crimson Sea (Kurenai no Umi). Having just grabbed this for $4.99 and also having found a soundtrack rip recently, I was absolutely stunned to discover how good the music is. Tons of variety and lots of high points throughout.
Drag-On Dragoon (Drakengard) is another one that stands out simply because it is so incredibly strange. I know that many people did not care for this music at all, but I found that it scored the action in a very unique way.
I'll have to think of some more....