Thief is an interesting game. Occasionally, gamers are asked to play characters that aren't exactly "good" people.
The monsters in Rampage are an interesting example of this. More recently, gamers might think of Kratos from the God of War series.
In Thief, Garrett is no Robin Hood. He doesn't pilfer to spread the wealth he steals only for himself and his own gain.
The audio directors for Thief felt that writing an epic orchestral score would confuse the message no heroic music for an anti-hero.
Composer Luc St. Pierre ended up writing a dark and ambient score, with harmonies that unfold slowly, shifting almost imperceptibly at times.
As dark as St. Pierre's music is, it's also quite intimate. At times, I found myself straining to hear what would come next. Rather than an annoyance, I found this an invigorating aspect to the score.
And remember that you can subscribe to the Top Score podcast on iTunes so you never miss an episode.