The models are way too plain imo. You use a lot of polygons without giving much detail at all.
The first one looks extremely sloppy. It might just be the [resized] render, but still not the best.
The second one has horrendous coloring. It is way too dark and will probably look even worse in-game.
All 3 grenades look fake, more like water bottles with straps on them.
The scope on the third one looks... weird. Remove or change.
If you're going to make weapons from CS:S, you need to be able to make them look as good as they do in CS:S.