I have played, or rather, playtested, this game, a year and a half ago, I think. Much as I hate to say it, it plays better without the princelings. With them, the beginning of the game seems to fall into an ultimately rather unenjoyable trading of all possible princelings. One can screw up, and lose an extra one or two, I suppose, but the moves are very stereotyped - basically forced. [And look how they play out - how does white do in the series of exchanges? Does black have a second move advantage? At this point, I don't remember.] It's an interesting concept and a very pretty setup, but it doesn't work well as a game. I believe the pieces need a little more distance between them at start, for starters. Maybe an empty 3x3 section or two added to the middle of the board would give some room for maneuver. Still, the extremely low movement ability of the pieces has a tendency to telegraph intentions.

I believe the problem with the princelings in this game is that they are too strong. Now, the king does have unlimited 3D freedom, which makes it almost uncatchable, so you might think you need all that extra power. But making the king effectively uncatchable, unbalancing the game, and trying to re-balance it by making the pawns into full, if forward-only, pieces, only makes it more unbalanced, I think. But I can't criticize without making some concrete and testable suggestions for improvement.

I'm promoting the 'Held King' rule this week for situations like the one here: a king that can move to 26 different locations on 3 different 2D levels. The friendly king may hold the enemy king on a 2D level by moving onto the same 2D level the enemy king occupies. Once this happens, the enemy king may not move off that level until after your king leaves that level. Both kings may freely move within that 2D level they both occupy, subject to the standard rules, including checkmate, but your king may freely move away on any turn, while the enemy king cannot, even to save himself from checkmate on that 2D level, and even if the enemy king would not be in check when on another level. This allows a conventional checkmate in 2D, at the cost of exposing your king to danger by moving up. Note that if your king voluntarily moves off the level, the enemy king can immediately follow your king to his new level, and then your king is held to the one level he's on. This solves the 'uncatchable' problem in a very nice way. 

I'd be happy to try the original and some reworked versions, if you'd like. I'm comfortable with the held king rule; it should work well in this game, given the nature of the board. I'm not at all sure about just adding a slice of board to the middle, making it a 54 cube 3x3x6. That needs real playtesting. For critiquing the game this way, Charles, I'll volunteer to playtest some revisions.