Nassua is alright. It's fun to go the "straw market". It's really a flea market filled with knick-knacks and knock off purses. You can get a decent deal on a fake bag (don't pay more than $20-40). Bring cash and haggle. There are tons of jewelry stores (like everywhere else in the Caribbean) and even a Starbucks.
I wouldn't recommend the mini-sub experience from Stuart's Cove.