With the advent of procedural music (that is, music where the song is arranged or mixed based on the player's actions), actual musical arrangement for a game has more or less become obsolete in parts. This is actually a really good thing because it means composers can arrange their pieces however they like in the actual soundtrack release, meaning that the album works just like that - an album. Additionally, the music being controlled by the game means that the game and the music are no longer really tangential concepts: The music is part of the game and vice versa.
The case in which this could be made for composers having more control over the soundtrack functions exceptionally well in an open-world game like FEZ (Polytron 2012, music by Rich "Disasterpeace" Vreeland). Sync is arguably the best example of this: The in-game version of the track Sync features a basic dance beat with a simplistic, constantly shifting melody as the player climbs a tower with disappearing blocks. The sound these blocks make act as on-beat musical punctuation, playing slow, dance-able arpeggiation, while more layers of music are added to the song as the player's altitude increases. Another track, Glitch, features the bassline of Sync as its basis, and samples a handful of other tracks from the game for ambiences, spliced-up beats and haunting countermelodies, reflecting its respective area's composition of all the other areas in the game. In the soundtrack version, Sync is just the basic song that plays while the player climbs the tower, but with a fadeout at the end into the simple rhythm provided by the disappearing platforms. Although the Sync room doesn't immediately precede the Glitch room, FEZ's open world nature allows the album to instantly cut from that simple rhythm into the glitchy break-beat of Glitch.
Another absolutely brilliant use of procedural music in a game is probably the most technically impressive soundtrack to any game I've ever heard: DOOM (id Software 2016, music by Mick Gordon). Opposed to the idea of track layering to indicate higher tension in the music, Mick instead played dozens of phrases per song that the game builds together into verses in real time, and during high-energy fights, the game quickly transitions to a similarly constructed chorus. The sound design to the music is even more impressive. Mick often used pure sine waves and white noise as the dry instrumentation for the music (at the request of id to not use guitars), which were then routed through four effects chains running parallel to each other. The first three would typically be long effects chains that totally distort the sound beyond recognition, and the fourth, a feedback loop sidechained to the very sound it was feeding back, resulting not only in a gate which controls the feedback amount (which is actually brilliant, I'm not sure why people don't do that more often. I definitely want to try it for myself), but a powerful reverse of white noise after every pulse. And then, as if that wasn't ridiculous enough, one of the effects chains was routed to the other two and the feedback loop before all being mixed together, resulting in a now-iconic juggernaut of a bass synth. And that request to not use guitars? He got past that - by convolving a nine-string with a chainsaw.
One last game score I have to point to, even though it's far from technically impressive (with many glaringly obvious instruments pulled straight from the Kontakt factory library, or the presets of FM8 and Massive), is that of Portal 2 (Valve 2011, music by Mike Morasky). This game has changed the way I make music forever, more than almost any other album I've ever listened to. This is due to two aspects of it: Sound design and themes. Sure, it might seem odd for me to commend the sound design immediately after pointing out its use of synth presets, but every synth in the game, from the light and bubbly out-of-phase sequencers to the rumbling, reverb-drenched growls sound diegetic, as if the computers lining the foundations of every room were producing the sounds themselves. The instrumentation is a key feature of the game's themes, too. Chapter 1's music, in the overgrown laboratories, features much more organic instrumentation, such as harps, strings and vocals, to something like Chapter 5, when almost all organic life had been removed from the labs. This isn't the only feature of the music that I'd call theming, because the more traditional definition with regard to musical motifs is employed (surprisingly frequently, but you really have to keep an ear out to notice). My favourite, more obscure example is when the bold cello strokes at the end of You Know Her become the vicious synth bass during the final boss theme, Bombs for Throwing at You while the bomb dispenser is active (and its cutting out whenever the dispenser stops is another excellent example of procedural music!).
Oh, wow. I sure talked a lot, didn't I?