What a brilliant little game... I'm a bit late with this one but I just got it with the Orange box (got the £5.66 deal on steam last weekend).
I finished it last night, thoroughly enjoyed it. I didn't find it to be particularly hard but I did find that you need to take breaks from it or else you would miss the obvious solutions... 5 or 6 hours straight is a bad idea. All in all, not very hard (if your awake) I think its time for the advanced rooms