I had Khao San Road for the first time a few weeks back - and I must say, I like Jatujak more. Now before people start to disagree, it could've been because I was at KSR's sister restaurant, Nanas because it was a Tuesday and they were renovating. I had the same thing at both restaurants, the signature Pad Thai with Shrimp.
I'm sure you can request the level of heat for your dishes, however I wanted to see what their default was. It was not spicy at all, but it was freaking delicious! For $12.95, you really can't go wrong. The portions are big, and the food quality is definitely there. I would recommend for anyone who doesn't want to spend too much on a pad thai downtown as the quality is better IMO.
My friend ordered the mango chicken which was really delicious (mango was nice and ripe) and thai iced tea. I'm not a fan of sugary drinks and asked if they could adjust the sugar level, but as expected they too use a pre-mixed thai tea. I had a sip and it was still good though :)