When I first listened to this 'album' I was a bit freaked out by it. Some of the songs make you feel like you are tripping in some way, what helps add to the trippy feeling is the way it's been produced, heavy panning from side, songs that really shouldn't be merged together being squashed on top of each other.
For example the first track (2+2=5 live) has the audience applause drifting onto track 2 (Remyxomatosis (Cristian Vogel Remix)) which is a studio track with synths remimisant to their 'Kid A' period. Don't get me wrong I'm not insulting the music production, mostly everything weird that you hear they somehow pulled off to make it a nice little creative touch.
Going back to what I said about the 'trippy' feel off the CD, alot of the tracks are very pessimistic, which Thom's vocals coming off as very haunting. After all this is radiohead.... so at points the 'trip' can be referred to as a bad trip I guess.
But not all of the tracks are downers, if you own 'hail to the thief' you will notice that they have redone 'I will', and I actually prefer the version on here, it's much more uplifting with real beautiful guitar parts throughout.
My personal favourites are 'Gagging order' which is one of the most hopeful and beautiful piece's of music Radiohead have ever wrote, and 'Fog (again)' which is another amazing song, which consists only of vocals and a piano, from the live performance Thom played at Le Reservoir.
Overall I would have to say it's a very mixed album, I personally don't like Kid A too much, so the 'electro' tracks I guess you could call them which make up half of the CD aren't really for me. If you are a Kid A fan then you will love this compilation, but for those looking for more of The Bends and OK computer you won't be too downhearted by the gems on this disc which in my opinion definitely make it worth purchase.