Overall the story was a really good hour-long episode. Unfortunately it was an hour and a half long. But there was a really good story in there somewhere.
The really good bits:
The script had some really good tension going once things started happening.
The Ice Warriors got a mention in passing. Not as good as actually seeing the kayaks on legs stomping around the set, but at least we know the production team haven't forgotten about them.
The really not so good bits:
The foreshadowing seemed tacked on as an afterthought; and in a few places the story seemed to drag just so they could pad the time out to an hour and a half.
Well, it wasn't quite a cop-out, and we get to see the Doctor in full-blown maniac mode at a couple of points (paraphrased: "I'm the last Time Lord. I don't obey the laws of time. The laws of time obey me!") All the story really needed was a bit of a prune and it could have been quite a bit better than it was. But, overall, it was still good.