Not a good investment. Who cares about the Uncharted artwork, no matter how limited it is?
I think I'd actually care enough to get a regular edition book, though even that's a bit pricey. The character designs in Uncharted 2 may be unspectacular, but the environments are a visual splendor.
The publishers appear to catered towards professional/hardcore digital artists, hence all of their books are expensive and (supposedly) high in quality. The typical gamer (myself included) would probably not get that much out of these books other than seeing pretty pictures, but then it's not geared towards us anyway.
As far as objective worth, the only real difference between their limited and regular editions appear to be the cover and rarity (and maybe a video and a piece of paper with signatures). And very few of their books appear to get sold out...There's apparently an "Art of Oddworld" with its own Folio edition. No idea when it was made, but only the softcover has been sold out, indicating that perhaps buying these as an investment seems like a really bad idea. If you're going to buy something like this, it's probably because you really
like this stuff and you have a lot of money to spend.