I saw it in York with my DS (just turned 5). I thought it was ok, the first bit was dire - Harry appears, introduced by Nana who is about 30 in a grey wig. Harry is also about 30, female, and a cross between Jeanette Krankie and Frank Spencer - gurning, lisping and pretending to be a 5 year old boy. The dinosaurs are stuffed heads poking out of a bucket, expect for Pterence, who is whirled around at the corner of the stage on a perfectly visible fishing rod... The voices are the real ones though, thank goodness - obviously pre-recorded, and that works well.
After some chat, and a rather groovy looking Charlie wanders on and off (again, yes, about 30...) they get to Dinoworld. Things do improve - Taury, Steggy and Sid are full size characters, although Patsy is reduced to a neck poking up from behind some scenery with a tail sticking out from the side, and Trike is obviously propped up on the same scenery with his "arms" hanging limply over the top.
The story's weak, as would be expected I suppose, with a few songs (not sure about the point of the Hokey Cokey in a packed auditorium...) with a break after about 40 mins then another 25 mins or so until the end.
If they'd had Harry in costume with a cartoon head on, like the dinosaurs (think Disneyworld characters, if you see what I mean), it would have been fine, but I simply couldn't get my head around the woman playing him and her annoying mannerisms. Having said that, my DS enjoyed it, so that's all that mattered.
Hope this helps!