I waited on this one, and I must say, I was blown away by the quality of my experience. It hooked me immediately and kept me playing for more than 40 hours, and I still didn't experience everything I could have.
Some people compare it to Bioware, and I think that's an apt comparison. It reminded me a lot of the older Bioware titles, like Jade Empire, Mass Effect 1 and Dragon Age Origins. It even follows a familiar formula: become some neutral-but-important figure, gain main quest, get faction-based side-quests, get companions, get companion-based side-quests, have up to two companions with you at any given time. The story is good and engrossing, and the characters are alright, but where it really excels is in revealing the world to you, which is very well-done on many levels.
The core of gameplay turns on combat, with a dash of stealth gameplay and branching dialogue. This latter seems more present in the early game, which rewards exploration, but towards the end I noticed it fell off a bit. Combat is well done, but there's a lack of variety when it comes to enemies, so it becomes somewhat rote after the first ten or so hours. Combat is also a bit on the easy side: consider increasing the difficulty.
The game is beautiful and has very few bugs, but it's clearly not a AAA experience. Assets tend to be heavily re-used and you'll run into a few bugs, but nothing really game breaking (though one prevented me from finishing a quest).
I really enjoyed this like I haven't enjoyed a game in a long time. I definitely recommend picking it up. I'll be paying more attention to Spiders from now on.