Finished the game last night
Same, about 9 hours at a guess while listening to all the talk (and doing stupid things to see what the game would do).
Got stuck on about 3 stages overall I suspect (ie: more than about 10 minutes, or what felt like 10 minutes anyway). One in stage 7 and 2 in stage 8 (some of those stage 8's, geeeeee).
The stage 8 one with the 3 turrets had me a good long time.
I posted before of what I thought of some of the stage 7 challenges, I should have saved that comment for stage 8.
Some parts appear consillized a bit, but I can over look it (portal positioning felt like a "snap-to-grid" at times, laser and items through the portal before it looks "formed")
Just have to say though, the ending was not a climax I was expecting, but then I can not say what I would have done to make it better.