I am furiously playing Diablo 3 to make my Witch Doctor more powerful. It is a testament to the power creep in the game that my new Witch Doctor was higher level after 1 week of play than my old one was after about a year and a half. I am definitely slowing down in my progression now that I am level 400 and I have all of my gear in place, but there is still plenty of progress to be made.
There is no cap on levels, though of course levelling speed does drop off pretty rapidly, and I can slowly work my way upwards over time. Right now I am still getting several levels per greater rift and that is eventually going to stop as my progression slows over time.
Gear is similar in that I have all of my pieces together but they can all get upgraded. Not only can each piece just roll with higher stats but it can also be ancient, which raises the caps on all the stats. Then I can get pieces that have better stat distributions and gain incrementally more benefits there. Each individual improvement takes a lot longer than the previous ones and provides less return but I can still see a long path of getting better.
I love the cube in terms of gearing characters up. The new cube allows people to target specific items and pour tons of resources into finding just the right piece of gear. It both allows people to assemble the bits they want right away to make their spec work and also means that people can farm for their improvements long term without just relying on totally random drops to make their stuff better. It feels better to be able to save up a bunch of materials and then pour then all into making a bunch of legendary scrimshaws to hopefully get a really awesome one than it does to just massacre mobs and hope that whatever drops happens to be my thing.
Targetting drops like this also means that people actually get their own stuff together without building every spec in the game automatically. With totally random drops you inevitably end up with gear for all the specs, and the cube allows me to crush my useless junk into chances for stuff for me. I can just collect all the things, or squeeze those things into more stuff for my main, and that is an optimization problem I enjoy greatly.
In short, playing D3 again, levelling up, having a blast.