In our opinion, it was more enjoyable than Typhoon Lagoon (not done BB yet so can't compare).
There seems to be more slides and rides there - and the Lazy River is the best. Well worth a trip.
Last time we were staying in St Pete's (2 years ago), we got a really good deal on a combined BG and Adventure Island ticket - to be used over 10 consecutive days. We did BG one day and then went back to do AI. We stayed in the water park until about 3.30 when we went back into BG for a quick trip to our fave rides.