There are two Bayon restaurants in Siam Riap. We ate the majority of our meals there (particularly since it was very close to our hotel). The food is good, and it’s a great bargain (as are most places in Siam Riap). Each dish is only $1 - $3 US, so a full multi-course dinner for two, including a couple of appetizers (satay with peanut sauce, spring rolls), perhaps a mango salad, a few main courses and rice, and drinks (beer and soda) was less than $15 US! The service was friendly, the décor spartan but clean, but tourists come back again and again for the food and prices. This is not fine dining by any means, but it's good food for a great price in a relaxing atmosphere.
I’ve read reports of this restaurant being packed with tour busses (the type of restaurant we try desperately to avoid), but that was not the case when we were here.