With two 27 inch lcds, and a thunderbolt external drive, it's been solid development machine. I can also boot an external windows drive to play PC games, with ok performance on the last gen of games. The form factor is great for traveling (I can stuff it in a suitcase and take it anywhere).
Last few weeks it's been kernel panicking a couple times a day (when under heavy stress). And it'd be nice to have upgraded GPU to play the latest batch of PC games (and VR).
I'm pretty disappointed Apple has made zero updates to this model in over 1000 days. Given how much use I'd gotten out of this machine, it's hard to say it's been a mistake purchasing it. But there's also not really much I can do to upgrade it since external GPUs don't really work with Thunderbolt 2.
My guess is the Mac Pro line gets quietly discontinued by next year. 15 yrs ago I bought a G4 Cube, some lessons I never learn.