Brilliant, immersive, relative! As a single-player this has it all, with a tiny lacking in story. After three plus play-throughs the game tends to be the same.
Where it has amazing potential to shine is in the multi-player arena. But again lacking, only a very small amount. With four players if you want to progress any of your companions story lines, one person will need to sit out while the companion story is progressed (usually no more than 15-30 minutes). Though add-ons can remedy this, not all players use these, and everyone playing needs to be using the same addons at the same version level. Something that should not be overly difficult for the developer the fix.
All-in-all best single/multi player game since NeverWinter Nights (WoW has nothing on either).
You can replay this game probably ten times over and discover something new about it every time. Every possibility has been thought of - you could pull off what you think is the most creative strategy known to man, and the game still anticipates it somehow. Plus, companions that feel alive, who act like people and not just characters. I'm so hooked