I went to Siem Reap in March! Definitely go to Angkor Wat at 4:30am for the sunrise! Make sure your tuktuk driver has a lot of water for you. It was HOT when I went. Also don't miss Bayon and the Tomb Raider temples! I paid $30 USD for the driver for the day. Probably could've gotten one for $20 but mine was very good. I also gave him a $10 tip which he was happy about.
Also visit a happy pizza restaurant if you like. Order your pizza "extra happy" if you want the special ingredient. :)
Pub street is cool if you like drinking, but I am not a big drinker. I got lucky and met some locals who took me to a local bar/restaurant and we had some good nights together.
Also DO NOT MISS the ice mountain ice cream shop! It's run by a Japanese couple who moved to Siem Reap and started the business a year ago. It's called Fresh Fruit Factory
RE: I ready to go Siem Reap trip