The three major things wrong with this game, that were made even clearer when I just replayed GW2 are:
1. The hit boxes are far less forgiving and as a result far less fun. In GW2, particularly Pacifism, you feel like a ninja, or like a fighter pilot in a cheesy action movie, swooping into tiny gaps and barely getting out of live, often wondering how you even made it out. It is exhilarating, and for me at least, a large part of what makes it so much fun. This is missing in GW3. You get hit way more often, way closer. It feels like your ship is slower compared to the blue diamonds, and as a result pacifism is harder, and in my opinion, less fun. This extends to the other modes but is less of a big deal in them than it is in Pacifism.
2. Enemy spawns take too long and are much more likely to happen on top of you as a result. The game decides where the enemies will spawn, and it won't be on top of you, if you are staying still. But you seldom are, so it seems much much much more of a gameplay element in this game to avoid getting spawned on, and I don't like that as much at all. It isn't a mechanic I find fun.
3. Again, mostly in Pacifism, there is a massive issue with the graphics obscuring information you need, namely whether or not the gates you pass through have killed all the enemies. The animations and graphics are so busy that you can't tell if you can double back through a cloud of enemies that you just blew up. You don't know whether or not there are some left alive waiting to kill you. This, again, makes you feel less like an awesome ninja fighter pilot.
These three things are not objectively bad necessarily, they make the game harder, and some may like them. But for me, they make the game much less fun and exhilarating.
I like the Adventure mode for the most part, and the obstruction that the various 3d shapes provide. I like the moving walls, and the different designed scenarios.
But Pacifism in particular has seen a massive downgrade for reasons 1 and 3, and the rest of the game is worse off because of 2, at least in my view.