My girlfriend and I ate at Chamkar three times during our visit to Siem Reap. We sampled a good portion of their menu and enjoyed everything. Some of our favorites included the wedding dip, amok puffs, mad eggplant lovers, and the mushroom pot. Everything is prepared fresh and the ingredients are top notch (we took a short cooking class with them and loved it!).
To respond to another reviewers complaint that the food was lacking garlic or chili I would say they are correct. This restaurant does not use as much as standard Thai or Khymer recipes so it's flavor is not as overpowering. I find that they balance ingredients very well to create unique vegetarian fusion dishes that you cannot find anywhere else. The dishes are all very refined and the French owner's influence is apparent.
They have two locations in Siem Reap both of which are excellent. The smaller location downtown is very convenient but has a slightly smaller menu. The larger restaurant has a beautiful decor and atmosphere but is slightly further out of town.
Finally word is that this is one of my top vegetarian restaurant experiences in SE Asia. Unique dishes, great decor (larger location), and friendly staff make Chamkar a must visit for your next trip to Siem Reap.
Cons: Slightly out of town (large location), A little more expensive