I was gonna make this thread earlier, but since I was still gonna get the game anyway I figured I may as well wait til it's out to prevent hearing the "you haven't played the game so you can't know anything" nonsense so we can maybe actually discuss the game.
The new slam mechanic, it's too powerful and oversimplifies the combat. Ghost catching is no longer a tug of war, once you reach full charge they're completely at your mercy. By catching just 1 ghost in your suction you can still hit all others in the room, whereas in LM2 you can only hit 3 at once and you have to grab all 3 in the same suction.
LM2 encouraged more thoughtful play, not only do you want to try setting up suctioning multiple ghost at once so there's less ghost attacking you, but you're also rewarded more money. Then there's the charge mechanic which rewards you with money if you captured a ghost using the charged succ, with the higher level charges granting more money. Additionally, charge succs also stagger the enemy, interrupting attacks and keeping them in place for a moment. You'll want to pay attention to enemy HP and use your charges in way that you can finish them off with the highest level of charge.
Now I'm not sure if the lack of an upgrade system is the fault of the slam mechanic, but it's an issue eitherway. Without upgrades money feels pretty useless, especially in the Scarescraper. In LM2 it's fine to go a bit out of your way looking for money as you're contributing to the team's upgrades, but in LM3 it's totally a waste of time except on the one mode that requires it. The story mode has a shop atleast, but unless you're a novice player too lazy to look up Boo/Gem locations online then money may as well be useless still.
Yes all Luigi's Mansion games are easy so it's effect on difficulty is kinda moot, but the problem is it's lesser depth. That's not to say there isn't any there, you do have to aim your slam and you need to be close enough. The one thing I learned from playing the game (not because this can only be learned by playing the game, evidenced by you reading this), is that there is timing involved, proper execution let's you get 5 slams. Still it's less involved compared to the traditional tug of war where you need to pay more attention to the ghost you're capturing and surrounding enemies.
The combat is still satisfying enough, I'm still enjoying this game, but I really hope they go back to LM2 style combat in future games.