The addition of 'z' plane movement/fighting was fun, I also appreciated the visual scale of a couple of the environments because it's not something I see alot in games:
Veins of Helios - how fun were the aerial faith plates outside in a giant space station.
Lunar Launching Station - emerging from Veins of Helios for first time and seeing the open space and the rumble of the moonshot cannon and, hey look, it's a planet.
I think I still play games with the awe and wonder of a 6 yr old...
Admittedly I gave up using the grinder. By the time I'd collected/created enough weapons to try for a blue+ I was too many levels above it to make it worthwhile.