Sushi CAN be very healthy but it can also be very UNHEALTHY! It all depends on what you order.
DITCH anything FRIED, BATTERED, covering in MAYO or thick sauces... And ditch sugary sauces like Ponzu or Miso Glaze.
While rice is okay, when ordering your rolls see if they have brown rice that you could sub in... Otherwise, order Sushi (fish over rice) and when eating, only eat 1/2 the rice under the fish... Or better yet, order sashimi - no rice, so delicious... Or order handrolls without rice, extra veggies and delicious fish! :)
These days restaurants have the option to wrap your sushi roll in cucumber and ditch the rice completely - sometimes these are called "sashimi rolls" - they're very delicious and nice and light. However, the wrapping on sushi (nori) is very healthy for you, so it's really a toss up as to how you want to order!
Personally I adore sashimi, hand rolls without rice and I order this appetizer dish called a Hamachi Kama, which is the neck of a Hamachi! SO amazing and full of healthy fat!