I would not try to pack too much temple-seeing into one day unless you're really into temple seeing. Spread the sights out over a few days.

Also, I went in an air-conditioned car one day, and a tuktuk the next. This was during the height of the spring heat, so it was very hot. I actually enjoyed the tuktuk more. The air-conditioning took a while to cool down the car, and just the breeze on the tuktuk was instant relief to me. Just my experience.

Oh, and on the tuktuk I swung by the land mine museum, which I think may have moved since. I wouldn't call it a 'must see' but it was an interesting side trip.

We inadvertently picked up a small child on the way out, he was crouched down at the back of the tuktuk, hiding. His head popped up when we were a mile or so away, and he couldn't have been more than six or seven. The tuktuk driver started yelling, and swung around, and we dropped him off again (he clung to the back the whole while and seemed to be having a blast), whereupon some sort of parental figure yelled at him. Poor kid. He didn't seem fazed, though.