EMI have, rather cynically, decided that now Radiohead have left them, they're going to release a Greatest Hits CD made up of some of the material from the 6 albums they recorded for them. Radiohead had no involvement whatsoever in the selection of the songs, the composition of the packaging, anything, and at any rate I would urge anyone interested to just buy the 6 albums for themselves - each (OK, maybe not Pablo Honey) a work of brilliance.
However, the Best of DVD is worth the money, purely because it is the first proper collection of Radiohead's music videos since "7 Television Commercials" back in the mid 1990s. Everything is in here, bar the Kid A "blips" (which wouldn't fit into a DVD format very well anyway). As well as the (typically brilliant) videos from throughout the band's career, it also includes two very rare videos, including what has to be hands down the most terrifyingly disturbing music video ever, "Pulk/Pull Revolving Doors and Like Spinning Plates". In some senses, the purchase price is worth it just to witness the fact that there's one band which has videos which can actually disturb you like that.
So yes, by all means, buy this collection, because there's not been anything like it ever. A cash grab it may be, but every cloud has a silver lining.