To really make those marines stand out I would do two things...
1) base them with sand, dirt or whatever fits your style and taste. I would loose the aqua blue some of them are standing on, looks like Jesus marines walking on water.
2) Washes. Especially over the silver parts. It will add depth and contrast to your models. Other then those little things, nicely done.
1) They will be getting a snow basing when I stop being such a lazy b...err...I mean when i have the time. Yeah.
As a matter of a fact, there were a couple of people over at MWG-forum who said that if I did not base these (especially the Chaplain) their computer monitors would join the fishes. True story.
2) Believe it or not, mosy of those models already HAVE been washed. It just so happens that the camera REALLY hates me, and eats the wash effect compleatly... -_-' Lucky me.
I still have about 30 or so Marines, two Rhinos, a Whirlwind and a Vindicator unpainted. i see after those if I finally would get the spark to base these guys (I really suck with bases...). Afraid we'll just have to wait and see...