We spent 4 nights here in December, while visiting Angkor Wat. We wanted to be in the town centre to experience local life, but once there, we found the town so dusty , dirty, generally chaotic and full of grubby looking backpackers that we were not sure it was an advantage to be near the town centre at all!
The hotel was beautifully designed but rather precious in attitude - a bit like an Aman hotel or a W hotel right next to third world poverty. I found it all rather incongruous yet I could not wait to return to its calm and restful atmosphere and its welcome hot water to get rid of that horrid red dust that penetrates every orifice of the body!

In short, advantages-

Large, well appointed, thoughtfully designed rooms with Aveda toiletries - we had a massive suite.
Excellent food, also in the cafe, although selection was limited at breakfast
Good central position from which you could watch the chaos of the town and visit markets and local restaurants easily,
Lots of helpful and well meaning staff - though sometimes understanding of English was limited
Attractive, well maintained pool area - though far too small for my liking
Good spa with excellent, well-priced treatments

Disadvantages:
-
They kept telling us that the place was designed by Bill Brenchley, or someone, a total irrelevance to us but obviously a major source of pride to the hotel. It was terribly design conscious.
A small site, so things couild seem rather cramped
Unappealing reception areas - minimalist gallery type design looked 'cool' but not at all comfortable or conducive to guests hanging around there - it was, not surprisingly, always deserted!
Mosquitoes - and loads of them - despite the hotel's efforts to get rid of them. Siem Reap is full of them.
There was no authentic Cambodian feel to the place -indeed it felt American; it was over-designed, though attractive nevertheless, and rather incongruous in its setting. It tended to emphasise luxury though it was slap bang next to extreme poverty.
The place was just too self conscious, design conscious and precious to be appropriate in this setting. It also had a rather irritating 'holier than thou' approach. I choose the charities I support without help from outside influences!
It was also very expensive, generally

Despite my reservations, I cannot deny that it is a phenomenal achievement to develop a hotel approaching international 5 star standard in such an unattractive, dirty and dusty area.

Spotless, faultless stay at Hotel de La Paix.

I stay 150 nights a year in different hotels worldwide, and this was one of the few occasions where I have nothing negative to say about a hotel.

Great concepts about sustainable tourism as well (example: No plastic non-recycled shampoo bottles - small copper flasks are refilled daily - it looks good and protects the environment at the same time!).
At Hotel De La Paix you are pampered, while your conscience is clear!

Great tour guides and drivers associated with the hotel.
Meric restaurant is awesome!
Breakfast is top notch!

Hotel de La Paix is HIGHLY RECOMMENDED!

My husband and I stayed here for 3 days while visiting Siem Reap and Angkor Wat. While we felt guilty about staying in such luxurious accomodations in the midst of such poverty all around us, we did love the hotel. There were so many nice touches throughout the room and hotel. We loved the ipod hooked up in our room that was fully loaded with music. We also loved the incredibly sexy pool and the amazing food at the restaurant.

The hotel provided a lot of options for things to do in Siem Reap. Our first concern was visiting Ankgor Wat . The concierge introduced us to a guide that cost maybe $10 for the entire day including a tuk-tuk driver. The guide's English was excellent and she opened our eyes to life in Cambodia. With another day to enjoy Siem Reap, the concierge provided us the opportunity to visit a local orphanage. They contacted a tuk-tuk driver to take us to the market, buy 100 lbs of rice, soy sauce, and fish sauce and go with us to the orphanage with the food. This was among the best experiences we had after traveling for a month throughout SE Asia.

Also, we had the hotel pick us up at the airport and were greeted with a sign, a really nice SUV, and cold towels and water in the car. If you're looking for someting posh - this is it!

Oh, I must admit - if you're a couple that has bathroom issues then this might not be your spot. The bathrooms are open to the bedroom with no doors! Don't let it stop you though - it's a beautiful bathroom...

This is a very "chic" hotel with comfortable spacious rooms. Everything is very well designed and the hotel itself does not disappoint at all. However there is still room for improvement on a management level:

Tour booking:
We booked a guided tour with transportation (Toyota Camry) at triple price of what major tourist companies charge for a similar tour. We expected more than average but got less than that. Transportation was in the oldest running Toyota Camry on earth with a malfunctioning A/C (would really have been nice with a working A/C in 35 degrees Celcius when our tour included 6 hours of walking up, down and around temples). Our guide knew a lot but his English was poor.

Taxi booking:
I couldn't believe this! This is the first hotel I have ever stayed in where they refused to get me a regular cab / metered taxi. We even had the phone number of the taxi company that operates in the airport yet they refused to provide any other transportation than their own which (again) was more than triple priced at 16 USD one-way (same old Camry again) or 25 USD one-way (new Lexus). Oh yes, they could also (they were actually laughing when they said it) provide a tuk-tuk for 5 USD. The official (probably government run) taxi company from the airport had a fixed rate of 5 USD one-way (March 2008 prices - nice modern cars with working A/C and English speaking driver). I can only recommend that you write down the number of the official taxi company and call and book your return journey to the airport before you check-out. I wouldn't be surprised though if the hotel employees scare your driver away or tell him that you already left so be prepared for a rip-off anyway.

Music in public areas:
Hotel Costes is nice and relaxed music but I can imagine that if you stay here one week or more you might get a bit tired of it - unless you're on drugs of course (which some guests seemed to be ?!)

Restaurant:
Please do not (I repeat: do not) go for the Cambodian Tasting Menu. Parts of it was in my case served in a bamboo container with a couple of live spiders underneath it (no - they weren't supposed to be there). The food was "interesting" but not really tasteful and I spent several hours on the loo afterwards with a diarrhea. The western food is great though - so is breakfast. Champagne (or sparkling wine?) is part of the breakfast buffet. I can recommend the cold cuts (and waffles with ice-cream if you have a sweet tooth like me).

Mosquitoes:
Mosquitoes are everywhere in Siem Reap. Although the hotel provides mosquito sprays if you dine outside in the evening, do mosquito "smoking" twice weekly or more and have candles with toxic fumes in the hallways you still have mosquitoes in your room. It would be nice with a mosquito net over the bed.