I really do love the aesthetics of the QuadPlay - that's where it really shines IMHO, but that's also a pretty subjective way to rate things, so YMMV. The piano black finish probably wasn't the best choice, since it's a fingerprint magnet (but so was the original control panel) but I really do love the way it looks while it's still clean. Thankfully, the no-nonsense surface is easy to clean, so that helps.
I also really like the feel of the joystick action, but I wish they had the teardrop style grip...this is another matter of personal preference. The buttons require a tad more pressure to depress than I would prefer, but I imagine they'll wear in, over time, and feel more to my liking - also, I'm sure I'll get used to their feel. I'm quite happy with the placement, count and orientation of all the joysticks and buttons - very nicely executed, but...
I don't understand why AtGames had to give up the spinners. There is plenty of room on the top of the panel for the spinners to be placed behind and slightly offset relative the player one and two joysticks. I hope AtGames will develop a v2 QuadPlay with placeholders for the trackball AND spinners. That way, the trackball and spinners from the standard panel could be transferred to the QuadPlay, which would then be compatible with the widest possible range of games without the need for non-integrated controllers. It'd also be nice if some pinball buttons could be recessed into the front face of the QuadPlay.
And that brings me to my final item for critique: the QuadPlay is not available as an up-front option for the Legend Ultimate. It's annoying to me that I had to pay for a control panel that I am not using (unless the trackball can be transplanted, but I haven't tried this yet). I really wish the Legend Ultimate would more completely live up to its name by offering it in either a 2- or 4- player variant, and not ask customers to sacrifice control types for player count.