Your favourite book based on popular game-series?

Banana.

I just read the Dead Island book. The characters personalities are a bit different from what they are like in the game but it still told a good story.

Myst book series. At least the first one. Never finished the second and haven't got the third.

I've read some of the Warcraft books. They were a pretty nice read and enjoyed them during my Wc3 and WoW-time. There is some interesting backstory of Thrall and Medivh in the books.

I've read some Warcraft, Stalker, Warhammer, TES books.

It's interesting if you like the game universe and want to learn about it more, but, sadly, some books are too much based on the game, bringing nothing new and, even more sad, some books are "non-canon", so you might end up with some controversial info after reading them (and I'm speaking about actual books, not just fan-fics).

I've read the first Halo book and a ghost recon one (it was a gift), those weren't bad, I enjoyed them.
I have an Alan Wake one as well but I barely remember anything about it :)

I liked Guild Wars - Ghosts of Ascalon pretty much.

I have only read Metro 2033,. I liked it a lot. I first read the book then played the game, and was disappointed that an awesome chapter was cut from the game.
EDIT: I had to google the chapter just to show you what gas been cut from the game. Spoiler for the book coming:

"The Savage Cannibals of the Great Worm Cult are followers of a xenophobic and technophobic society mostly comprised of brainwashed children"

...
Would have been awesome.

Haven't read book based on game for so long time, but I have read some years ago many times book based on Baldur's Gate series and I loved it.

I rather read books of other kind.

A Starcraft trilogy called The Dark Templar Saga

They're not based on "video" games, but The Thran and the Artifacts Cycle from the Magic the Gathering line and a bunch of the Vampire: the Masquerade novels are really good. Both of them have also spawned video games, but the card game and tabletop RPG came first.

Or if you want to count comic books as "books", there was a decent run of the Archie Sonic the Hedgehog comic before Knuckles got a cyborg girlfriend from the future who was also related to him.

If you want to count in-game books, some of the ones in Oblivion are pretty entertaining.

If you only want video games that later spawned real life novels, well... I've never read one. There aren't actually that many out there.

The only game related books I've ever read were Splinter Cell: Checkmate and Splinter Cell: Operation Barracuda.
They are really good; well written and the characters are recognizable and well-handled in my opinion. I can recommend, if you're a fan of Splinter Cell games :)

I've seen those Assassin's Creed books, too.
Never read them myself, but I think it may be very interesting. Maybe even better than the games :D

Here's a small list of my favourite books based on games:

Warhammer books are really great. If you like fantasy, you can read:

• Blood bowl series
• The adventures of Florin and Lorenzo
• Malus Darkblade
• Gotrex and Felix

For Warhammer 40k, you have:

• Everything written by Dan Abnett, especially the Eisenhorn and Ravenor series
• Gaunt's Ghosts (by Dan Abnett too)

You can also give a try to Metro 2033 which is really amazing. And don't forget the Witcher series by Andrzej Sapkowski.
There's the Shadowrun novels too, some of them are good.

metro 2033 was awesome

Halo and Mass Effect books are very great.

Hellgate London is crappy game, but the books are good.

The Withcher and Metro books are great, but they are not based on games, games are based on books. This is like to say that Lord of te RIngs books are based on LEGO Lord of the Rings :)

I've only read the Diablo Series which are based on the game. Well they aren't really based on the games but the story is strongly related to the lore and stuff. I really loved the books.

I read the "Hellgate:London" trilogy which is quite good . Got Warcraft,Diablo and StarCraft books which are also quite good but not as good as Hellgate's one :D