Came here on a whim one summer night and left very pleased. In my opinion, this is very comparable to Khao San Road with slightly lower prices. As usual, I ordered my favorite thai dish, Khao Soi. The quality is very comparable to Khao San with exception to the viscosity of the curry, which was made noticeably less thick at Pai. My only other complaint (which really shouldn't even be a complaint) is that that there were an overwhelming amount of beef compared to noodle and personally, I prefer to have balanced ratio of each.
Not to mention, the resto has a very cool and hip vibe with enthusiastic servers, which is always a bonus. Pai is your best bet for thai food if you want to skip the line for Khao San Road.