Dear people of the interwebs, from now on out in this thread I'm just going to be giving out realistic CnC, no flowery words or anything like that. I'm going to be harsh, but not mean. Just wanted to make that clear. I was going to make a topic for it but decided against it when I realised that nobody would post there. Anyway, here I go.
@Beckie It's needs sharpening in some areas and part of the background is still centered. I blame Peewee, the guy who made your tutorial. Sometimes the people who make these tutorials are just plain wrong, so try and stick to the basic principles of composition. The reason why we place key elements on the intersects rather than the middle is because the eye is most naturally drawn to these intersects rather than the center. The only other criticism I could give is to not follow the tutorial so closely. Your sig is pretty much exactly the same as the one used in the tutorial. The tutorial is there to teach you the techniques, not to teach you how to replicate their sig.
@Harcore The C4D one really isn't one of your best. This is entirely because of the C4D itself. It really doesn't fit with the rest of the sig. It smothers the Crysis render and the C4D has pretty much become the focal point which really isn't what you want. As for the smudging sigs, you should try and add more colour to them. It would probably be helpful if you looked up colour schemes(or just read the colour part of that tutorial I made).
As for the smudging itself, it needs more depth. Add layers to it, get some stocks and smudge from there. Smudging is a lot more time consuming that a lot of people seem to think. Mess around with the layer modes and the strength of the brush to create different textures. As a little help,
here's a .PSD of a smudging tag I did recently, and if you really want to see how Pro's do it, I suggest downloading
this .PSD pack from deviantart. These are pretty much the best smudging sigs around, and you will be able to learn a lot from them. Of course, you're not as good as them and you probably won't be for a long time, but it will still help.
@Luc Not one of your best luc. Aside from the render, it's monotone, and would best if you accentuated the blue from the helmet in other parts of the sig. Also, too much blending. The render is barely distinguishable from the rest of the tag. You could probably solve that while you're messing with the colours.