I have somewhat of an unhealthy obsession with both the Iron Man Hulkbuster armor and LEGO, so in 2015 when they released the first licensed set (76031), I bought it immediately. That set had quite a few things that I thought could have been improved (feet, upper arms, overall flexibility, etc.) but it was the first of its kind and has been on my desk ever since.
In 2018, just before the new Avenger’s: Infinity War movie movie was released, LEGO unveiled two new Hulkbuster sets. One of them is an ultimate collectors edition (76105), has 1300+ pieces, stands over 9 inches tall and is $120.00. (My personal man-childness is not quite at the level where I can convince myself that’s a justifiable purchase.) The other set (76104) ties directly into the Infinity War movie, was much more reasonably priced, and looked like it was enough of an improvement from the 2015 set that I went ahead and bought it.
Having now put them side-by-side, the 2018 set is a huge improvement in the feet and torso, but the legs seemed stuck in some half-squat position and the upper arms still seemed a little barren. So, I decided to cannibalize the 2015 set to make some improvements to the newer one. I was also away from my normal LEGO resources at the time, so I literally only had those pieces available to work with. Overall I think the legs are much better, I made some slight modifications to the scale and flexibility of the arms, and I added more details here and there with spare parts. Now the torso is probably too small for the scale of the limbs, but beefing that up will have to be a future project. This whole idea was largely inspired by the amazing work of flickr user ChubbyBots and his amazing work building custom LEGO mechs and improving official sets (like this!).