We visited recently over Whitsun (2 adults and our 8yr old). We have visited before and once again thoroughly enjoyed the day. I agree with the comments made by previous reviewers that Gulliver's is ideal for children up to about 10-12yrs. Above that and you'll struggle to keep the adrenaline pumping for too long.
For me the main positive is that the whole day was pretty stress free, with no lengthy queues, free parking, friendly staff and a general calmness about the whole place. Yes it's very hilly, so can be quite tiring in places, but I do believe the layout contributes to the overall charm of the place. If the hills become a problem, just do what we did and work your way down the hill, get the chair lift back up to the top, and start all over.
The attraction itself has plenty of rides etc on offer and we were there for pretty much the whole day. We took some food with us, but did indulge in a few snacks while we were there and they were reasonably priced and of good quality.
Regarding value for money, the admission cost was around £40 for the 3 of us, which I consider excellent value for a full day out.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC