We stayed at the Khemara Hotel as part of a package tour. If we 'd had a choice, I would have probably chosen a different hotel. But Khemara hotel isn't a bad option for a couple of nights. The rooms are huge and very clean. Most of the staff speak decent English and are helpfull. The pool is pretty small, but it's a great place to relax after touring the temples. We had dinner at the hotel on our first night there, and the food was pretty good - but you're better off eating out in town, it's cheaier and there's more choice.
The only complaint I have about this hotel is breakfast. After reading the reviews on tripadviser, I was anticipating a good breakfast, but on our first morning I was suprised to find that all they had was eggs and a small selection of breads and fruit. I think that this was due to the fact that we were there off-season and the hotel was less then half full. On our secnd morning there, though, the breakfast was completely different, with a much larger choice of food, and as good as most of the previous reviews say. So we were probably just unlucky to be in the wrong place at the wrong time :) But it only lasted for one day.
Overall, Khemara hotel is as good a place as any to stay at while seeing the temples. Most of the hotels in Siem Reap - apart from a number of the more expensive ones - seem pretty much the same - from the outside at least, so it really looks as if there's not much difference where to stay. If you're looking for a clean room and a nice pool to relax at in the heat, you won't be dissapointed by the Khemara.
