Opened my TT version today, here's my 2 cents...

Before I start, the TT version has fixed the issues with the Headmaster not coming out, as have recent Hasbro releases. No issues with floppy wrists on mine either. The extra paint apps also really add a lot to him IMO. So yeah, if you're a Brainstorm fan (which I am), it's worth getting the TT version.

Anyway, thoughts on the toy in general.

He's big. As in, he towers over other Voyager figures, including older- and taller- Voyagers (eg. Classics Optimus Prime or Springer). In a way he's almost too big - he looks kind of out-of-place amongst most other Classics-type bots. This is the size that Cyclonus and/or Lugnut should have been, especially in bot-mode.
It also really makes you miss the older, larger Transformers we used to get. *sniff*

He's also very, very simple. If you need interesting/clever transformations, then skip this guy. Being a Transformer is kind of tangential to his main charm/selling point.

His Alt-mode is, well, kind of rubbish, albeit kind of reminiscent of a Star Fox Arwing, which I rather liked from a nostalgia point of view. Even so, the way HasTakTom just sort of left his arms and legs as great big chunks of kibble really lets down the alt-mode. The Headmaster, while a nice idea, is also, well, crap.
None of which really matters to me, because...

...the robot mode is just beautiful. This is IDW Brainstorm, looking like he just stepped right off the pages of the comics in the same way as Springer, only more so. As a Transformer he's kind of a let-down, but as MTMTE Brainstorm in toy form he's beautiful. Nicely poseable, solid construction, able to loom over and look down on other Autobots, perfect looks...all he needs is a briefcase. He really is less a Transformer, and more an action figure that happens to transform, with a neat little gimmick that pays homage to his original toy/character to boot.

If you're an MTMTE fan, or a Brainstorm fan (for me he's my favourite MTMTE character from what I've been able to read, and I like a lot of the characterisations in MTMTE), then he's a must-have. If you like HTT doing homages to old toy concepts and want to encourage them to do more, then he's worth picking up. If you like big TFs with nice robot-modes and don't care about the alt-mode all that much, then he's a nice addition to a collection. Otherwise, he's either a Pass or an Only-If-Cheap.