I found it very easy to get to grips. The only downside I found was due to the lack of a particle engine doing any high quality 3D effects was very hard. I did manage to do my own basic 3D particle engine but GLB really needs the ability to put alpha'd images in z-order quickly and not via GLB code.
Also I came across a couple of bugs with screen2world and world2screen on the iPad. I *think* one was sorted and the other wasn't. I haven't checked the latest beta as I've had no time to spend recently on game coding at all
I would love and also pay highly if GLB's 3D engine were a little more up-to-date. But for what it is, it's a decent little multi-platform 3D engine that's speedy and easy to learn.