I lived in Thailand for a year and I can easily say Khao San Road has some of the best Thai food in the city.
Everything is simply delicious from the squash fritters with the wonderful dipping sauce to the tasty shrimp to the fantastic Khao Soi which I recommend ordering with beef.
The only downside is that it can be tough to get a table. Sometimes you need to show up, put your name down and leave for an hour or two until your table is ready.
Everything is so so good.