They aren't bad in my opinion. But their songwriting is overrated, and their technical prowess is decent, yet uninspiring. Chris Martin is a good frontman, but he's not exactly a brilliant singer (and the falsetto cop-out is a fact, as one poster pointed out).
What is unique about my opinion of them is that I am usually quite digital in my thinking, meaning I am a love/hate music fan. I don't hate Coldplay by any stretch, but I can't say I love them. In fact, I feel that way about most of their songs, with a select few falling under 'love' or 'hate.' I'd say 'like,' not 'love' is accurate on the whole.