Adaptive music is good. BAD adaptive music, however... *shudders*
We have Lego Star Wars at our house, and that game has "adaptive" music. When you're just walking around, the different areas have different music. When you fight, it plays something more dramatic... like a fast-paced version of the SW theme song.
Here's the problem- it does that even if you're invisible, or a Jedi ghost, or shooting from behind, or even if most of your enemies are dead. Problem? YES.
Shiny. Let's be bad guys. :D