I finally got around to checking this place out. Pai is super popular, so it gets very busy during dinner time. I'd highly recommend you make a reservation - otherwise you'll be waiting easily over half an hour for a table.
The restaurant is huge on the inside and runs like a well-oiled machine. Everything from getting a table to getting your food to getting the bill is designed to handle a LOT of customers. The atmosphere inside is very loud and boisterous - not quite bar levels of rowdy, but certainly not a good place for finding some peace and quiet.
Food-wise, they have quite a few good-looking Thai dishes. I tried the moo ping (pork skewers) and the gaeng kiaw wan (green coconut curry) with fish. They were both delicious. Portion sizes are a bit on the smaller side (aka they're normal-sized, rather than oversized like most restaurants). There's also a nice selection of interesting cocktails and drinks, though I didn't try any.
Overall the experience was fun, and the food was tasty. I wasn't a huge fan of just how big and loud the restaurant was - at times it felt like the restaurant was just herding cattle. But if you don't mind the crowds and the noise, then check this place out sometime.