As with most Americans, I was first turned onto the books via the video game. Having first assumed the books were written AFTER the games, I passed. I've yet to read a "post-game" novel that was really worth anything (except Rapture based on the Bioshock games because this novel is not based on a specific game which is nice). Anyway, after I discovered that the games were based on the books, I decided to give it a try. And I'm thankful for it! As was mentioned in the current #1 comment, the publisher's description is actually wrong! I'm not sure I would even classify Geralt as an anti-hero. He's a straight up hero through and through (at least in The Last Wish). Sure he collects money for the monsters he kills, but last I checked, our police officers and military don't work for free (groups I clearly consider heroes). Geralt was pulled from his family as a child and forced into this life. Instead of taking the typical Witcher life devoid of morals and emotions, Geralt often finds himself doing quite a bit of good merely for the sake that it's the right thing to do. Again, that's a Hero in my book. You will clearly see the "lesser of 2 evils" theme repeated which was the inspiration for the games (versus Mass Effects obvious good/bad decisions), but this does not negate the often purely "good" decisions he makes (e.g. defending the weak, helping someone in distress, etc.).
The writing (a translation I believe) is quite good! Again, this a really a coherent collection of short stories. There is a minor thread, but it's a thread. This is not, however, a self-contained true "novel" (though I'm anxious to read his actual novels). As has been mentioned, this is a VERY dark world. It's gritty, harsh, and unforgiving. The language is mildly rough (meaning there is definitely the full spectrum of 4-letter words, but they are used infrequently and appropriately... versus modern games that seem to swear strictly for the sake of swearing. Hopefully we grow out of that adolescence). Some stories are twisted takes on the original Grim Fairy Tales (which are a joy upon discovery); others purely created.
If you like character pieces, you'll thoroughly enjoy The Last Wish. If you're a fan of fantasy, you'll be pleased with the world of the Witcher. If you are a gamer, this is hands down the best game-related piece of literature I've stumbled across (again, mostly because the game followed the stories and not vice versa).