Nice work on the conversions, quite a bit of effort going into a cool army. I did the same thing as you for my Tzeentch marines by combining the Possessed and the CSM's together and it is a simple thing that looks fantastic.
Now for some constructive criticism that is not meant, in any way, to offend you regarding the paint.
Simply: you have too many colours going on. Perfect example is this guy here
Red, purple, white, silver, gold, black, etc. Too much on one model UNLESS most of those colours are used as small highlights and to pick out details. You should only have two main colours with a third as a contrast that take up the majority of the model. The rest should only be on very small things like purity seals, lenses, etc. In general, all the trim should be the same colour and this includes the eagle, skulls, etc that come on the model.
Personally, I would have painted the model red like you did but also the backpack (colour #1). Trim would look good in the gold (colour #2) with a slight darkening from a chestnut ink wash. The third colour would have been the boltgun metal on the gun and also done on the poweraxe, in between leg and arm joints, mouth grill, a couple antennae, and washed down with a fairly heavy black ink mix. From there all the areas are covered in your primary colours and then you can use the other colours to add different touches here and there. The blue on the scope is great and the hose would look awesome with a green colour. In fact, since the model is primarily red, I would use green in 3 separate spots on the model for the "3 spot method" which is using a contrasting colour in 3 small yet separate areas of the model to draw the eye around more.
Another thing I would do is check out Pandas Colour Theory
tutorial regarding colour choices as it is DAMN helpful and something that can help anyone to mix colour schemes better. I use it all the time actually.
Anyway, those are some tips for you if you are will to receive them