The demo dropped late yesterday and I've been having a ton of fun with it so far. Getting used to palamutes/monster riding/wirebugs/silkbinds/weapon changes is a lot, but I love the new degree of mobility all players are afforded. And monster riding in particular is undeniably fun.
The Insect Glaive didn't really experience any major changes coming off of World, but that's largely fine by me. Its silkbind attacks are a little underwhelming, but I know there will be others in the full game. Other than that, and as someone who didn't play much World, I'm having a lot of fun just zipping through the air with vault + wirebug combinations.
I also love how they incorporated endemic life and gathering items into these maps. The map itself feels vibrant and colorful, but not so large or detailed that you get lost in it. It really encourages you to run around and explore for its own sake, instead of haplessly looking around for your target monsters. (I definitely don't miss Paintballs.)
I have not tried the other weapons out extensively yet, but the Hunting Horn underwent a complete retooling which makes it much more user-friendly and less "support-oriented." I'm sure it'll be hugely popular this time around. Other than that, the Hammer and Heavy Bowgun seem to have gotten major boons, while the Switch Axe and Longsword seem largely untouched.
Oh and the game runs great so far! I was worried about framerate drops in handheld mode (I have a Switch Lite) but I haven't experienced issues so far.