So I just played a decent amount of the PS4 beta for World over the last few days and my impressions so far are extremely positive.
I made sure to try every weapon at least once, and every single one of them is very satisfying to use, even if I didn't delve too deeply into all of them.
Of particular note are the changes they've made to the gunner weapons, (which I've personally never found overly satisfying) that have made them even more viable choices than before. The simple third person perspective and more dynamic ammo types go a long way in making them a lot more fun to use, and I'll almost definitely be using the Light Bowgun quite frequently when I get the full game.
All of the other weapons have been given similar additions to movesets (save perhaps for the Hunting Horn, which has received comparatively minor, though still notable, upgrades from my understanding of the weapon) that add to the overall feel of polish and dynamism.
While the demo downsized the quests quite a bit for the purposes of the beta (they significantly reduced monster health, lowered the time limit to twenty minutes, and possibly reduced attack damage, likely to help ease in newcomers) taking on several subsequent quests gave me enough time to understand the new mechanics.
One new mechanic in particular that I was somewhat wary of was the Scoutflies. Previously, I wasn't too fond of the idea of Scoutflies, as I thought they would make it far too easy to find the target. However, after spending some time with it, I came to realize that the seamlessness and overall greater size of the maps makes them somewhat necessary. It would take a great deal longer to track down the monster you are hunting without them, as the maps are so large and intricate. It could potentially take quite a large chunk out of the time limit before you were finally able to engage the monster if not for the Scoutflies. And it's not as though they are immediately capable of leading you directly to the monster, some preemptive investigation is necessary to level up your flies to the point that they can take you to the beast. However, the flip side of this is that once you have leveled them up to that point they can tell you exactly where the monster is from then on, which may be a turn off for some, who like to track down fleeing monsters on their own, a sentiment that I share.
I do have some worries that some of the new weapon movesets may take away a significant amount of challenge from the game, though it is hard to tell with the beta downscaling everything. If nothing else, they reward playing skillfully.
The multiplayer works very well, as is to be expected from a Monster Hunter game, though I did have some server issues that will likely only be present in the beta. As usual, the game allows for many fun moments that can only be achieved in such highly situational co-operative play, enhanced by many of the new gameplay mechanics. My personal highlight was when I managed to look like a total badass in front of one group after I slid down a hill and severed a Anjanath's tail with a well-timed leaping thrust from my Switch Axe.
The maps are another excellent addition to the game. As I said earlier, the maps are seamless and vast. They also weave on themselves in incredibly intricate and complex ways. The environment of the Ancient Forest is immensely detailed and full. Just about every section of the map has several exits and entryways that connect to other sections, and not always in the most obvious ways. One can easily get lost in the foliage-filled forest's twists and turns if they're not paying attention. It will definitely take my ADHD brain quite some time to grow fully accustomed to them.
Then on the other end of the spectrum is the deserty Wildspire Waste, which is much more open, aside from a few gorges, cliffs, and one small forested section. But the map design is still just as complex from what I noted (I didn't spend nearly as much time exploring the Waste as I did the Forest). In a central area of the map there is a large sandpit which, when opened, leads down to a cave containing a rather fearsome looking Diablos. I know this because I saw the Diablos from a distant cliffside that happened to have a nice view of the inside of the cavern. This view might prove useful to future hunts if your quarry happens to be prowling around beneath the ground. I did find an alternative entryway to the cave later, but didn't spend a whole lot of time looking around, mostly on account of the Diablos trying to rip the head off my shoulders.
From my impressions of the beta, I think that this new entry is going to be a very promising step for the series. It may not turn out to be perfect on all counts, or be able to please all fans, but for my part I believe I will enjoy it quite a bit, and I hope it will draw in a host of new participants to the series.
TL;DR: The beta is really damn promising. The mechanics are implemented very well for the most part and the maps are well designed, if not a little confusing. I definitely plan on getting the game. Also I cut off a big fuzzy dinosaur tail while sliding down an incline and it was the coolest **** ever.
Will edit if I remember to add anything else.