Given it a bit more of a play now, so I can give impressions.
Playing it entirely docked, honestly, it's great. As others have said, it's obviously going to have the lowest resolution and frame rate. It's stable and distant objects and structures are visible with detail naturally improving as you get closer. No Pokémon SwSh popin here. The main issue is that lines can get jaggy up close which, given that the art style is heavily line based, which might be off-putting. That said, you'll be spending a lot of time in motion in this game so it's less notable.
As for the rumble, it's...subtle, but frequent. That's the best way to describe it. Walking and running causes no rumble, but changing gravity, moving items (including clattering a cube on each stair while running up some) and running water all give a little rumble. One thing I've noted is that falling from a small height gives the exact same feedback as falling from a great height. The audio makes note of you falling from a massive height, but there's no rumble feedback from you dropping, only the same you get when landing after running off a smaller ledge. It's not an issue, just something I noted.
Oh, I completely forgot that it does become more constant when you're at the end of each level and things are up and running. It's not much more intense, but it is more frequent, which is good.
EDIT: Right, I've finished it now. First of all, what a trip. Great game. I'm all for PSVR version if that ever comes out.
As for performance on the Switch, it does dip a bit towards the more densely packed areas at the end. There's also one bit of big pop-in when heading towards the final area of the game, but that's about it. Otherwise, a nice and stable game.
Well, stable in the FPS department. It's still an absolute trip otherwise.
