Didn't get to play as much as I'd have liked, just hitting 8th level, but that was a lot of fun. Felt a lot like old times. I barely played D3, so maybe some of the things I view as new were present there, but lots of quality of life stuff. How potions work, access to the town portal, not having to identify items, free respecs until level 15... all good stuff.
Queue times were next to nothing on the Xbox and it did lag and kick me out a lot, but that's not too surprising for the beta. Didn't get to party up and go that route, but I'm unlikely to do much of that anyway.
I'll wait to buy, probably. Replaying ME3 will take me a while then I'll do Jedi Survivor. Unlikely I'll need anything between then and Starfield coming out. So D4 probably shows up in my world next year sometime?
If there's another open beta I'll jump in again.