4 is definitely harder than 3, between the demo and the footage of area 2. The enemies are more dangerous and you're handicapped with a smaller squad. This alone isn't saying a ton though, 3's combat was truly trivial. But enemies falling from the ceiling is a pretty big sign it's going to ramp up quickly.
I think my biggest concern with the new camera is that it makes the game harder to play for the sake of fancy graphics and no actual gameplay benefits, which feels pretty un-Nintendo. I have no idea what other upsides it was supposed to have, but this lower angle perspective made the Sun-Speckled Terrace much more disorienting than I remembered past locations being, and I relied on the map a lot. Outside of 3's multi-tasking mechanics, I only ever used the map to check for stray Pikmin in past games. Here I never have any idea where I am because there are so many paths, some are obscured by walls, the base is moving around constantly, and crucially, the camera does not stick to one orientation. I'm glad the Pikmin can navigate on their own now, because I sure can't.
Like, you know what the worst camera I've ever encountered was in? Trails in the Sky, a top-down, turn-based RPG. I cannot accurately describe how awful that game's camera was, but one crucial facet of it was that unlike superficially similar games, like say, the DS Dragon Quests, the camera does not have a static default overhead orientation that you are meant to view most things from. It's a small FOV, constantly spinning and turning and melting my brain to slag, and I very quickly had to adapt to navigating entirely using the minimap because at least the directions stayed consistent there. I'm worried Pikmin 4 might have a much milder version of the same thing going on where it's impossible to maintain a consistent perspective on the environment anymore because the camera is close in behind your character now. Hopefully I just have to get used to it...