I have read so many great reviews about Ninja here on TripAdvisor that I decided to give it a try on my last trip to Koh Samui, and I always heard "don't judge a book by its cover" , Yes, totally right.. Don't judge it, the food was delicious, the personal friendly and very alert, it can get very busy so don't get there too lat on peak hours or you'll have to queue for a place. It was actually the first time I go back more than 3 times to the same spot, I usually enjoy trying all different options and usually pick the beach because it is so nice there, but Ninja was so good that we were back many times, and plan to do it this year too. Not so charming but I loved the open kitchen, get to see them preparing what you are about to eat is always nice.
Give it a try and you wont regret, and the prices are awesome. A tip: as far as I remember the portions are so great so get many different things and do your own mini Thai buffet like we did, our little son loved to get to try different things and got some new favorites!