There's already not enough minor gods as it is, Act 10 is missing a mid-act boss entirely while act 9 only has 2 additional bosses. Garukhan is a pretty cool fight, but the basilisk is disappointing especially after the lead-up with the petrified soldiers. Most of the zones in act 9/10 don't even have a unique zone mob. I'm fairly certain there will be changes to some of these zones/bosses in the near future, once the dust from the 3.0 release has settled. Malachai had 6 relatively tough fights before him in short succession, Kitava had absolutely nothing.
Fall of Oriath was always marketed as a revamp of the leveling structure, with little to no changes to the endgame. I don't know why people are surprised that the endgame feels like it didn't change much. It wasn't supposed to.
Harbinger feels quite similar to Invasion, only you don't get oneshot from offscreen. The unique items are all pretty weird but most of them have decent uses for at least a couple of builds, which is how uniques should be in my opinion. A bunch of them have stats that aren't available on a single other item, which makes them actually unique.
The Beachhead provides great XP and drops a shitton of maps and the change to the loot in the final fight was desperately needed. The returns from running a biscos and a bunch of iir gear was fucking insane. I did a couple of T15 Beachheads before the harbinger changes, even running a very strict filter my game was starting to lag before I finished the encounter. I accidentally pressed alt once and was immediately greeted by my desktop because the game absolutely couldn't handle it. I also got about 10-15 T14+ maps out of every single run aswell as 1-3 harbinger orbs, which made chaining it quite easy. That's not supposed to happen, so I can understand why they changed harbingers the way they did. I also get way more harbinger/annulment shards since they changed the harbinger drops, so I don't really understand why people are complaining about those changes either.
Harbingers themself are fairly easy, at least for the build I am running. However I've already heard plenty of people complain about the obelisks/new harbinger, getting oneshot by the laserbeam and stuff like that. It really accentuates the importance of not being a glass-cannon, an idea which a lot of people in non-hc leagues seem to be very uncomfortable with. As a league mechanic it's about as intrusive as Invasion, only without the offscreen oneshots. You can also easily skip them if you wanted to.
All in all I quite enjoy the league. My biggest concern is with how absolutely fucking garbage people have become ever since breach/legacy. The entitlement is incredibly strong with most of the people on the forums/reddit, complaining about every single little thing.
Stuff you regularly hear for example:
-"The Boss hp nerf was stupid, it now takes me 6 minutes to kill a boss"
-"I got oneshot by the harbinger lasers, they don't even drop that much loot if you finally kill them"
-"They nerfed density on strand by at least 75%, wtf GGG?"
You can easily see how most of these people started playing when getting easy defense through ES was a major issue, double-dipping was running rampant and running T11s was better for XP than anything else in the game. Well, now things have changed a little and all these little crybabies can go fuck themselves and play D3 if they want 20 uniques per boss, the impossibility to die thanks to "cheat death" mechanics on every single fucking class and 15$ necromancer DLC instead of a 60$ Supporterpack that comes with 55$ worth of points and a set+pet.
This entire expansion was supposed to revamp the leveling to draw new players in, looking at the player count they absolutely fucking succeeded with that. Now they have the time to look at other things again, and I am fairly confident the next challenge league will be way better than harbinger. I sure hope they incorporate many of the new bosses and rework the atlas a little, the endgame has become quite stale since the release of atlas and no leveling experience is going to make up for over a year of no new challenging endgame content (shaper release was the last one).