I love how you've gone the extra mile to customise them, and the fact that you've put the thought in - that alone makes the most difference with these, more-so than painting, converting etc.
Again, the painting is superb. For someone who claims to havepainted so little, you seem to have caught on fast
(then again, your older stuff was well painted too, so...)
Here the bubble bursts. I don't think (from a fluffy point of view) that bare arms would be even considered by marines. Not only does it compromise their armour, it would leave them weaker and more vulnerable.
It also raises the question of "Have they nailed the shoulder pads to their arms?"
Also, the lack of backpacks is a little disconcerting, but hey ho.
You've no doubt noticed your Heavy Bolter has one armoured arm and one unarmoured arm too
A great set of models, with well-excecuted conversions, a great paintjob and a lot of thought and care.
Well done =)