My last thoughts on D4 and a bit long...
I have my three characters above to T2/T3 and started a cataclysm druid which is about a 20 now. All 4 are squishy so I'm either choosing some weak builds or they nerfed damage resistance. Builds seem to rely more on DoT effects than before so you almost always chase that on your weapons.
The loot filter is great once you figure it out, but that isn't too hard. What you don't notice is even the loot is of differing quality. Take a legend/ yellow for example. Some loot will have 4 stats and some will have 3. You might see a great piece but it is missing an entire stat which is okay for leveling but not something you want to invest mats in building up.
Very few builds are new. A few are modifications. Some do not use an ultimate. Unlike OP spiritborn and paladin when released, the warlock is a bit underwhelming to me, even when compared to basic classes like a sorcerer, druid, barb, etc. Your 3 S Tier builds are a sorc, rogue (death trap again...), and a whirlwind barb (again).
Aspects and mats...did Blizz miss these. Being unable to target farm aspects and instead relying on drops or obol gambling is painful, especially at lower tiers because the drop rates are so low. I think I was in T1 on 2 of my characters before I saw my first offensive aspect. The aspect also turned out to be useless for my build. Now you're caught where you can't progress without aspects on your build, but the drop rate at lower tiers is trash. Two ways of gambling for aspects is to upgrade your legendaries/ yellow at the cube or through the vendor and obols. The problem is mats for both are also slow in dropping at lower tiers, so I've spent more time at T1/ T2 trying to get my build going than I ever did leveling.
This makes the game grindy, way, way more grindy than before. Chasing war table bounties breaks it up a bit, but you need those bounties to open some great traits towards loot. Again...that grind.
Blizz needs to buff aspect drops and the cube materials. The average guy playing 30-60 minutes after work will quickly tire of the grind with a slow trickling payoff. You can tolerate a squishy build if you know you'll have the mats or aspects to upgrade. Only the functionally retarded like myself will stick around and spend hours playing at range in the hopes of getting a good drop, which is only 1 out of 10-12 necessary pieces. Boss farming is kind of the same but you need keys to open their chests and the guys have a low drop rate.
Good luck with the grind.