It's the first band I really got into, every song I can play in my head right now (except maybe a few unreleased ones). IMO it's a pretty good alternative/experimental English rock band and has some pretty nice stuff. Sometimes a little proggy thing, like concept albums (lot of them), 7/8 bars (Glass of Water), criticising the society (Such a Rush is a very good example).
Chris Martin is an excellent pianist and guitarist, and comes up with nice riffs (Amsterdam comes to mind instantly, really a gem!) and sometimes surprisingly good chord progressions (I love Twisted Logic chorus). Guy Berryman sometimes has nice basslines too!
The rest is IMHO just average, Will Champion is a good drummer (like in Fix You), and main guitarist Jon Buckland is not really that good, though sometimes very alternative/experimental/renewing/original (Daylight for example, pretty weird for the first time).
I really love most old stuff (I really like The Blue Room EP) and actually everything until Viva La Vida (with A Rush of... at the real top), from then it's downwards, being A Sky full of Stars being the worst (the nadir(?)).
I'm really interested in what you think of them!