I really love Khao San Road. It turned me onto Thai food. Flavourful, spicy, and clean-tasting (my stomach can be sensitive). It's a smart restaurant ... they know they don't have the service to check your glasses, so they give you giant Cokes if you order them. I'm happy with that. It may not be the most elegant, but it's practical. Great casual place with excellent food.
Thing is, the wait is just not cool. It's always there, apparently, and you can't rely on eating when you want to. My boyfriend and I would come here so much more often if it wasn't a crazy wait even in the middle of the week.
Go to Sukhothai instead. Even though it's run by the same people, the food is somehow just a little off ... the pad thai is a tad mushier, and less spicy. The wait for *food* can be too long (actually ... time for another review). But it's good enough and you almost never have to wait for a *table*, so it doesn't really matter in the end.