I went for a second time to Khao Sarn. The first time I thought it sucked, posted so, and got several rebuttals. So I tried it again. Worst Thai restaurant I've ever been to (out of about 100). Worst restaurant in Coolidge Corner. Pretend Thai food for people who don't like authentic Eastern cuisines.
The restaurant is very nice, and the dishes are plated much better than is normal for Thai food. The wine list is "terrific." If you'd like a (cough) $170 bottle of 1997 Lynch Bages with your (let me guess) pad thai, it's there for you. No need to worry about spices ruining it--Khao Sarn's version of Thai food is no more spicy than French.
I started with fresh rice paper rolls. Hard to screw these up I would have thought, but they were almost completely filled with thick iceberg lettuce. Sure, there was a nice crunch, but that didn't make up for the watery mouthfeel and the dissipation of flavor. The sauce was fine, but they may as well have brought out Ranch dressing. The worst fresh rolls I've ever had.
My main course was the red curry seafood. This sort of resembled a Thai red curry--I noted some coconut milk and a few specks of red pepper. It was a very pale liquidy orange. The coconut milk was highly watered down, destroying the creamy texture, and there was just a hint of red curry flavor. I'm not sure whether their goal is to purposefully remove the flavor or save on ingredients, but whichever, the result is disgusting. As a positive, the scallops were fresh and tasty and the mussels were a nice addition.
I wanted to order mango with sticky rice but I decided I wouldn't throw any more money away. Khao Sarn sucks, I'll say unabashedly, and Zagat's sucks even more for giving it's food a 25--absolutely ludicrous.