I've heard a lot of comments, over the years, about how Radiohead have pretentious fans... but in all the Radiohead forums I've been a part of, everyone is just plain awesome.
I've seen people come into these forums /just/ to bash Radiohead, and 99% of the reaction is; "Oh... well you obviously don't like them. That's cool."
I think the pretention comes from people who refuse to like Radiohead because it was so fashionable to like them for such a long time... after all, you can't be an indie kid if you like something that happens to be a critical darling, can you? Nope... can't be independant unless you pay way too much for new clothing that looks worn, and then try to 'out-obscure' your peers with your musical tastes... can you?
To be as objective as I possibly can, even though I'm one of the biggest Radiohead fans alive, I have to say this;
Their musical composition, ever since The Bends (and /especially/ OK Computer) is amazing. Some people call it genius... I've even been known to say the same... but to tone things down, and take them out of the realm of fanboydom, their compositions are unique, experimental and intelligent. Unlike many bands they have constantly evolved. No two albums have ever sounded alike, and no two songs on any album seem similar to one-another. They put on one of the most entertaining live shows in the business, bringing their electronic influences, classical instruments and energy to the stage with ease. Watching Johnny Greenwood literally dash across the stage during live renditions of 'Idioteque', playing with dozens of different mixers/samplers/EQs/etc... it's truly awesome (in the proper sense of the word, not the overused one).
To be objective, Thom's voice would probably bother a LOT of people. It can take some getting used-to, and depending on the song, it can vary greatly. People who've only ever listened to Paranoid Android, Just, Creep, Knives Out (etc) are probably going to think he's a terrible singer... but when you listen to the last minute and a half of 'Let Down' or songs like 'Pyramid Song', 'I might Be Wrong', 'Go To Sleep' or 'In Limbo', there's little denying the man has an INCREDIBLE vocal range.
Radiohead is not for everyone, obviously... and claiming that they are reshaping music is too bold a claim for even the biggest fans to make. They are, however, undeniably talented, experimental, and should be respected for what they've accomplished. Anyone claiming that they 'suck' is simply being ignorant.