Fun: "Differing from the ordinary in a suspicious, perplexing, quaint, or eccentric way"
I use this definition because it is in the old/original definitions that we find a words true meaning.
So fun is essentially, something weird, something different viewed in a positive manner. The honest truth is you guys haven't done any weird.... It's ordinary...
When the Uber fights came out in D2, they were weird, strange, but very fun. Now we have more Ubers(I don't like how you did them) that don't even have minions on the way to them... keys drop rates blow, considering it takes 5 stacks to get to them.
Honestly its too predictable, just like the fact that you brought up ladders. Do not implement them, please. Ladders where fun at 1st, until your character became non-ladder and pointless to keep. No one wants to play any video game as if it were a job(unless that actually is there job). Then there's that moment when you realized all the best items were on ladder(extra stupid, one of the d2 crews biggest mistakes, this made me leave d2 for good)
Give us something new, or ask me: soon. I have a million idea's that would improve the item diversity, the diversity of the gameplay, etc. But this point though, as I have offered my services for free in the past. I would only offer my knowledge after a contract was signed and my fee schedule was approved. As it is I would rather save what I've learned from your mistakes, and good ideas, and make my own ARPG, as many now have.
But I'll give you a tidbit, the uber fights:
The whole just fighting boss/spawns isn't rewarding enough. After spending all that time getting my machine I feel horribly ripped off. Add some dungeon space in there to work up to them(yes just like d2). Also, more events, but uber events, very rare events that spawn in the place of any event/area of a given act. But these don't spawn only spawn Uber bosses. They spawn Uber packs of improved white(Giant Improved Packs of white mobs), or Uber Elite pack itself(certain packs types only evidently always the most dangerous monster types), Uber champion packs, even Uber Unique's. Now I'm not saying I don't want to see a Uber Diablo fight. I do. I just think it should be done differently. The only Uber fight I would redo is Clone Diablo(Diablo Walks the Earth). But you've got some great minds I'm sure you could make this even funner
Now I want to add 2 things in, Legendary Packs(still elite, 1/1000 will have a legendary affix, a 5th affix)
This legendary affix will give a 50% chance to drop a certain legendary(Legendaries will have tiers linked to these affixs) with 5 stacks. (this is an inferno only quality, pushing in more endgame content while adding afew new and dangerous attributes)
Now we have even higher risk situations that are very random that can't be farmed easily with a good chance at a reward. (You could test bots on your own servers and make these legendary affixes that defeat their mechanics)