The key to Placebo's sound is singer/guitarist Brian Molko, whose impersonation of a woman goes far beyond his appearance and into his singing voice.
His trio brings together various influences -- the epic, noisy "Chicago sound," late-'70s prog rock, and late-'80s "college rock" -- but boils them down into fairly conventional, guitar-heavy melodrama, with the sort of opaque and angst-ridden lyrics usually found in that genre.
That's not to say that Placebo's sound is boring; churning guitars and direct, heavy basslines give the album a good deal of strength, and Molko is able to write moving, gritty melodies and fairly clever lyrics.
Placebo may sound like a mix between the Smashing Pumpkins and Rush -- and the levels of melodrama on the album may stretch far beyond most people's tolerance -- but it's well-written and performs enough variations on those genres to keep it interesting.