They have a lot in common with another band I like, Porcupine Tree. My view on these things can be warped and inconsistent, so fwiw:
A Rush of Blood to the Head was the album that really cemented their trajectory upward, where they were, for a short time at least, considered perhaps the greatest band in the world with a messianic frontman (they held this title for about sixteen days before U2 reasserted itself into this role)... then came X & Y. For me X & Y was the superior effort for me because it had a lot more rock and bombast, while on Rush of Blood it's much more atmospheric and restrained. I like atmospheric, but only when it has the lyrics and vocals to match. I don't think they have particularly good lyrics (or particularly bad ones either), but dude's vocals start to grate after a while, especially when they're the only thing really going on in a lot of songs. So I would say start with X & Y and if you decide you really love them go backwards to their other albums.
