I went a few years ago, and enjoyed myself, despite the coaster being closed. Having said this, I wasn't an enthusiast back then, and so don't know what I'd think of it now.
I'd say go if you happen to have a spare day and live close to Portsmouth (as the park's small, you can do the boat crossings, the park and go for dinner in a day easily), but don't expect thrills or even many rides at all.
I personally prefer Robin Hill.
Burniel | Great at theme park knowledge, not so great at designing signatures.