I used Gallery2 so far, outside Joomla, no integration with 1.5 (at least not one that actually works), but was not satisfied.
Along comes JoomGallery. There is room for improvement, nice-to-have-stuff. But it works, it looks smart, it integrates nicely with my CSS. I'm just happy and eager for it to come out of beta.
Support: I had a few itches, they got answered. I got one real problem, they answered immediately and solved the problem.