Development-wise, TBM was a total mess in my opinion, but it still had some great things in it.
The most hilariously amazing thing for me was pre-nerf bard Dichomatic Psalm <3. Keeping everyone topped off on mana and even doing a decent heal was great — totally OP, but totally amazing.
The mirror to flip between versions of Sul Vius was a cool concept. Unfortunately, zoning kind of takes away from it though... 10s timer on the mirror now makes that even worse. /grumble
I enjoyed doing the missions in a broken state. It made them more challenging. Damsel of Decay was one I remember in particular. You pretty much had to beat her after she warped downstairs the first time. After she warped back upstairs, I believe she would get stuck inside her pedestal where you couldn't hit her anymore, and on top of that, her out of range script would kick in and start DTing people.
The inclusion of type 5 augs on gear was a nice addition.
Lyssa`s Darkwood Piccolo from the Plane of Hate raid is probably my favorite clicky in the game. I love DA clickies.