Very solid start, you really have the basics down. The legs are just perfect, and your bases are especially well done for a flock/gravel base. Great job on the lenses too. Overall you have fantastic brush control, or at least are wise enough to clean up your mistakes when you finish. Great job.
I wish the upper body shading/edging could match that on the legs, especially on the pauldrens. The pauldrens are one of the most visible parts on a
SM, and these are very flat compared to the rest of the mini. You've done a good job using black edging on the pauldrens, but there is no highlighting or shadowing. Either paint them with a gradient or do some edging around the rim of the blue. Or something else if you have an idea.
There are also a few places that could do with a wash in the painting process, notably the guns, chest aquila, and purity seals. Your whites are too stark (chest and gun ornamentation for example), going from strait black to very white, and would look less like a painted miniature if you based them in a grey or bone and highlighted up to white.
The purity seals are very flat and could a wash and more highlighting. Purity seals really stand out on
SM considering their size, so you really want to do them right.
This isn't a painting issue, but consider not painting the top cover of the bolter metal. Your guns are currently fairly bland and it is an opportunity to bring some contrast to the gun, and show off your edging technique. Traditionally UM's guns have a red cover, but black is common too, or green to complement your shoulder trim. Do an image search for 'bolter' and to see what I mean and get some ideas.
Finally, look up some tutorials for skin or painting faces, it is a weak point of your sergeants paint job. Out of the whole squad the sergeant's face is going to draw the eye, you are going to want to get it right. Here is one of my favorites:
http://www.youtube.com/user/awesomepaintjob?blend=1&ob=4#p/u/22/-ac1oLYiyi8
Hope I'm not coming across as negative. These are really well done, above tabletop quality certainly. Good luck, can't wait to see more.