I have a confession... I haven't seen Inception yet. I have, however, picked up the OST and I love it.
I'm a big fan of the Batman osts that Hans Zimmer collaborated on and the Inception ost is in a similar vein... albeit maybe not as dark.
Zimmer has a real grasp of contrast - soft & loud, slow & fast, build up & slow down, light & dark etc and this ost is a perfect example of his approach. I also love how he combines orchestral with electronic. It makes for a more immersive experience.
It also makes beautiful headphone music for a morning commute.