General update for those undecided: Having played more of Grimrock, I definitely feel it's overall a better game and a very solid FPRPG. If anyone felt that Grimrock 1 was too difficult/puzzley, this one has a much better difficulty curve, with a lot fewer brain teaser puzzles, and more sort of 'adventuring puzzles' (with obviously the right mix of brain teasers thrown in). There are only a few times when I've felt that things weren't fair (compared to a number of times with the first game), and there's a lot more exploring to do and loot to get.
Whilst it sounds like a small change, having charge up powers (double damage, leech life, ignore armour and so on) on most weapons really adds more tactics. You have to keep the button pressed for a second or two to charge it up, and in that time you could have probably done two or three normal hits/dodged out of the way.
My only dislike is that levelling up is still incredibly bland, but it does have the bonus of making it difficult to completely gimp your character. As a caveat to my last post about it running well on an old laptop, I do get quite a bit of slow down in some out door areas. It's about manageable, but definitely a bit sluggish when there are lots o' monsters around too.
Just for others who might waste their time - as mentioned, treasure hunting/digging seems to be pretty much only where you get told to go in notes. I've dug around a lot of areas which looked promising (dead ends, alcoves, places that look different) and haven't found anything. I imagine that at one point they were going to have lots more stuff hidden around, but probably (and rightly) felt that it would drive people mad having to dig everywhere.