Techmarines inhabit a strange world of split loyalties with one foot in the chapters of the Emperor's spacemaines and the other in the cult of the Machine God of Mars. As such I always thought of them as somewhat akin to a cowboy builder or electrician who can talk a good fight but that you secretly suspect might be in over his head and telling porkies about the job at hand. I'm sure that's not the case and that no techmarine has ever looked at a totalled landraider and sucked his teeth or commented that the previous work done on a rhino was that of a "right amatuer".
Seems to me that the issues surrounding the RT era apothecaries sculpting are non-existant with the techmarines. Their poses are good, the detail fine and the proportions just right. In addition the theme of massive tools and the shoulderpads in the form of talons on the right and exposed tech on the left are something that unfortunately (in my opinion) never carried over into later editions of the range.
With the techmarines I thought that it was important to keep away from effects such as bone and gold detailling and instead to make them seem more functional. Growing up in Sheffield I was surrounded by museums full of machinery from the industrial age and most of these towering engines seemed to have been painted a deep green, so it was a logical step to apply that same colour scheme to the techmarines. Also I feel an odd echo of the "Green Goddesses" the military fire engines used by the British army.
I have to admit that I was a little disappointed this guy didn't have the same kind of oversized tool as the others (I'm still hunting for the techmarine with the massive monkeywrench!), so I console myself with the idea that he's looking at his wristchron in exasperation. Perhaps he's waiting for a transport that's late or cursing the servitor that he sent down to the stores to get him a screwdriver the size of a garden rake.