I am 5'3" and a size 12-14 depending on the brand, and it was a very tight fit for *me*. The lap bar crushed into me on both rides. I had a small camera backpack (1/2 the size of a regular backpack easily), and it barely fit by my feet. We saw larger guests on it as well, so it's doable...but if you can leave anything you're carrying somewhere (a locker, with a stroller w/no valuables, etc) - I definitely would. DH is taller than I am, and he was also uncomfortable.
We enjoyed the ride...it's worth riding, but space is definitely very very tight.