I just fought the HR3 boss (low-rank final boss). Well, fought him three times because the group I was with we all needed to rank up.
It's... actually pretty fun for a final boss, unlike *cough* Gogmazios *cough*. He's not some stupid HP sponge and he's exciting while doing cool things while looking super badass. He's also really mysterious and just all around well-designed in general. There's not a moment where you're just sitting around going "well, it's time for him to do the thing and we can't hurt him while he's doing the thing".
I have to give props to the MonHun team for making all the new monsters in this game a really nice experience to hunt. They're all great.
I wish there was waaaaaaaaaaaaaaaaaaaaaaaay less gathering quests though. Jesus Christ they really went overboard with it (which is why I gave up on it previously). Some of the quest sequences are really stupid too. For example, right after you hunt your first Yian Garuga fight your reward is you get to fight another Yian Garuga. Literally just the same quest twice in a row. Why? There's so many examples of this. Another one is after you hunt a Khezu, you unlock the ability to hunt two Khezus, which unlocks the quest to do a Khezu Hunt-a-thon (I think this quest chain was intentional though, as the Yukumo Gal is trying to justify to you why she's doing this and apparently your character is not amused).
I'm also staring at the "Hunt Three Nibelsnarfs" quest right now.