Just did a few runs with my game face on, think it was 6 or 7 runs, 3 victories. Difficulty seems fine overall, probably made a bit harder by most of the special weapons being underpowered with the new energy system. I fought the Labyrinth boss again and won this time. The most difficult bit seemed to be the homing shot that chases you around, I just ended up tanking through it for the most part, although that was probably a bad strategy. One thing about this boss, I like the multi-phase thing, but it seems like you might've got the phases the wrong way around. It seems like a more climactic progression would be to go from the four corner enemy form to the big central form, rather than the other way around.
Edit: hmmm, just realized it's not a multi-stage thing, everything spawns at once......probably just disregard the above comment then!