I'm a bit surprised by the negative reviews, I think this place is pretty good, considering it doesn't have to be (being right in a very touristy area).
I must admit, the first time I went, I didn't love it. I forget what I ordered but I think it was simply not my favourite. I came back a year later and was in Bangkok for several months, and this became one of my weekly dinner spots. I tried several (at least 6 other places) in Bangkok to compare the sushi, and this was the best. The one spot that was on par with this quality had VERY high prices, especially for fish.
The service was good, I got a table right away (I usually came at 5:30pm). They quickly learned who I was and smiled and greeted me nicely. Food came quite quick for me. English was not perfect for every server, but the menu was easy to point at and if I wanted to do something complicated, there was always someone around that would understand me.
I did not ever try the all-you-can-eat, so I'm not sure how that is. I did a la carte and quite enjoyed it. The tempura was not my favourite, but the rolls and the sushi bowls were great. I frequently got tuna/avocado rolls, salmon/creamcheese rolls (liked the asparagus!), crab (kani) creamcheese rolls, and the tuna don.
It's not cheap by Bangkok standards, but on par with sushi prices from where I live, so didn't shock me. The rolls were a good size, and the tuna don came with at least 8 huge, nicely sliced, tuna sashimi pieces.
The restaurant was a nice size and right off a main road, so I think the venue is good. There are traditional booths which I thought was nice. It's also clean! And tea is refilled frequently, which is a bonus. If you eat at the bar upstairs you get a nice view of the busy street, if you are alone and want to people watch!
So, maybe the all-you-can-eat is not great, but try the a la carte. You might be surprised.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.