HTTT is so horribly underrated. It's such a fantastic album. Stylistically, it's my favourite in their discography due to its sheer diversity and as far as songwriting goes, it's almost on the level of OK Computer. IMO it's significantly better than Kid A, which is generally viewed as the band's second best.
HTTT has so many classics. It covers many different styles brilliantly. It has great pieces of hard-hitting electronic music (Sit Down, Stand Up), more ambient Kid A-sounding songs (Backdrifts, The Gloaming), beautiful piano-based songs (Sail To The Moon), simple but pretty ballads (I Will), catchy acoustic rock (Go To Sleep, There There), and even a song with very singable lyrics and Pink Floyd-esque background music (A Wolf At The Door). And of course, we can't forget Where I End And You Begin, which is easily one of the greatest songs Radiohead has ever written. It's so dark, yet catchy with an almost alien lifeform-like sound to the synthesizers. That song absolutely blows me away every time I listen to it.
Overall, I think the album is incredible. It's as good as anything else they've ever released, IMO.