A friend recently checked-in here on Four Square noting that the service was abysmal. They are 100% accurate. That being said, Khao San Road has the tastiest Thai food I've ever had (and I actually don't like Thai at all).
The food was delicious. According to people I know who have been to Thailand, the dishes are the most authentic they've had.
The Gaeng Kaew Wan aka Green Curry was stellar. Perfectly spicy, TONS of tender chicken, but could have had some more vegetables other than bamboo shoots and green peppers. The Street-Style Pad Thai was so delicious. It's unlike any Pad Thai I'd ever had, and what I imagine Pad Thai is supposed to taste like. Really peanut-y and smokey flavour that we couldn't stop raving about.
Hopefully they work out their service issues. The server debated with us about our credit card being a debit card, when it was clearly a credit card, and ended up double-charging us. Annoying.