WHOO BOY DO I HAVE THINGS TO SAY
first of all. I had a fucking blast, I hunted Rey Dau and he was a blast. There's a lot of changes coming from MHWI and MHRS with my mains, but I can confidently say i'm enjoying them all.
The biggest complains are mostly the performance. I have the recommended specs for the game, a 2070 Super, but even with the right settings I too am getting awful LoD loading and weird glitchy artifacts. It's just graphical though, the game itself plays fine.

Opinions on Weapons:
Switchaxe: My baby, my main, my beautiful swagaxe. The changes from World and Rise are not substantial but it's enough to make axe mode muscle memory almost completely ruined. The Rise overhead opener is now a main move, but it's on A instead of X. Instead of having easy access to the uppercut axe move, X + A is now your counter (offset?) move. Switchaxe gets to keep its counters, but sword mode's only accessible after heavenward flurry and I don't see myself using that move often.
I really miss when the phial ticks buffed Axe mode like in Rise, it really emphasized going back and forth between both modes to boost damage. Now it's back to sword mode ungabunga I guess. I really hope the game isn't focused on counters because I don't play switchaxe for countering, I play it for dodging, and I noticed how much easier it was to dodge monster attacks. Either the hitboxes are smaller or the iframes are longer, I don't know.

Lance: When I found out that the Lance Counter was replaced with Power Guard, I was about to be really upset until I realized that your regular guard is a counter and you can perfect guard and counter any attack. You can also choose which move to follow up with and that's INSANE. My muscle memory is unfortunately stuck in World mode where I try to counter after every third poke, but once I get used it I feel like this is going to be the best thing to happen to Lance since World. You can counter after a third poke with A and charge up a fourth poke, but I really don't see myself trying to counter mid combo like that. I got a ton of power clashes with perfect guards and I see Lance being one of the top weapons of this game for that reason.

Complaints:

I've played monster hunter since the Wii days and went back to the PSP games. I am very used to using the d-pad as a camera control. World and Rise had options to restore the d-pad as camera control in game but now the d-pad is unable to be set to camera control anymore since its used for Seikret control. I really hope they give us an option to have more control on what menus are on what button because not having d-pad camera control is really screwing me over. :/

The environments are gorgeous... when there's not a sandstorm or Rey Dau is in the area, which is only like 5% of the time. I want to see all the beautiful colors of the environment but that's impossible when the sandstorms turn everything into uniform grey browns. Either turn down the environmental effects or make the sandstorms less common, idk