Yeah, I think the best example would be Space Marines in Relic's Dawn of War II series. Like some of the problem with W40K art and other media- they just look like plates of metal slapped onto a general shape that don't look that thick or protective. This looks like it has actual mass to it and thick armor at that.
My only complaint would be as similar to others, the lack of Chapter iconography and distinguishing features. The only guess I could really make is this being loyalist Emperor's Children from the aquila on the front, which isn't commonly worn by modern Chapters.
You do need to draw MK IV more often though. The helmet looks awesome. You ever thought about drawing a Reaver from the Sons of Horus?
So, this guy is pretty damn impressive. For a bust he's got a nice and simple pose that immediately grabs the viewers attention. There's also nice amount of detail in his armour to avoid the 'Bob/Clone/press mould' syndrome that can so often afflict 40k space marine art. I will admit however, that I feel there's something missing from this guy... it might be a lack of ornamentation or squad/chapter insignia that could breathe some more character/life into him but I'm... I'm not quite sure... In any event, this is a pretty solid effort and has produced a very impressive bit of art, you should be proud. (I do especially love the perspective with the Bolter he's wielding, you've nailed it!)
It really was my pleasure, I assure you sir. your art in general is pretty damn cool, but I thought this particular piece really deserved comment due to the visual impact it makes on the viewer. sort of a "You will look at me", the image draws you in, grabbing your attention. you don't find that often in 40k art, you get a lot of piece battles and heroic poses... but very rarely can a 'simple' picture of a space marine draw you in, in the way that this image dose! Suffice to say that I don't normally go out of my way to comment on Deviantions, one word or one line replies feel kind of hollow. It's my personal opinion that if you going to say something, make sure it counts. Don't just put 'good, yay', that being said, that's simply my way of doing things!