Definitely a popular sushi place downtown and you are likely going to have to wait in line during peak hours. I personally don't rate it very high when it comes to sushi places. In fact I can think of about 10 others spots I would pick before Sushi Island, but I believe it's the only one in that College area so I can see why it's a chosen locale.
The all-you-can-eat factor is definitely a plus but when it comes to rice just how much can one eat? That stuff expands and leaves you bloated, and if you order maki rolls you will notice they really pack on the rice to get your belly full. I've actually never had anything other than the all-you-an-eat deal so I can't really comment on the rest of their menu.
Service is kind of so-so. You never really know what you're going to get sometimes. The vibe also seems to lack a certain authenticity and quaintness that I'm used to with quality sushi places. You won't necessarily be disappointed with Sushi Island but there are definitely better options in the city.