I've been to Sushi Square on a couple of occasions and have been disappointed both times. The first was a couple of weeks after it first opened and we hung out with the consulting chef. The second was few months later and a new chef. Both times we had the same qualms: the lighting was too bright, the space unfriendly and the food a little bland. The gazpacho was very good however. Other than that, the food and the restaurant in general seem uninspired.
I started a discussion on sushi on east side of Miami here:
We've now tried Oishi based on several recommendations and thought it was good but pricey. I also liked Sushi House (also on Biscayne just south of 163rd) but my wife was not as enamored.
Hiro (on 163rd St. east of Biscayne) is pretty good.
Sushi Republic (Surfside) is also decent.
I'm not a big fan of Siam Bayshore's sushi, although I like their Thai food. Nor Benihana even though it's very close for me.
Katana is fun for the boats, and there are some things I really like there (they put a little shredded mild onion or something and a little dab of mayo on top of the salmon which I, for reasons I can't fully explain, think is just fantastic) but my wife thinks it's a little dingy.
There's a new place on Biscayne around 72nd St. called Sushi Square which I haven't tried yet.