Ahhhhhh, Sigs...they bring back so many memories from when i was a young teenager.
Anyway, for starters; you want to avoid stretching images (it ALWAYS looks bad), hold shift when you're resizing to keep them in the right proportions.
and that desktop is all about manliness eh? :P
Nice work, but I do have a complain about the aspect ratio on the avatar and siggies.
i agree with everyone else's comments and i will also say that a slight amount more work could be done on blending but other than that they look good....
yes
aspect ratio stretching (1, 2 and avatar), like said, use shift + drag to retain shape
oversharpening where it's not warranted (no 2)
default "outer glow" (cream with "screen" or "normal" layer effect) on avatar would look better being less intrusive and bright (maybe different colour)
the text in the corners is a very strange colour that doesn't fit (1, 2, 3 and the wallpaper, though i do like 3 [good texture] a lot more than 1 and 2... the text morphing looks out of place at the edge of the image). Try finding fonts in dafont.com and adding them to your works to make them more unique :3
your background in 1 is pixelated (the blood splatter and aura). Try looking on deviant art for some really highres blood/paint splatter brushes to add to PS. Would help with 3 too.
Your wallpaper's background has too much going on in it. I would recommend finding a barren wasteland image, messing with the color levels to make it look more EVIL. Then use brushes and layer effects to add in some lightning, dark clouds etc.
And this is just me, (personal preference)... but the fact the 3 characters have nothing to do with each other makes the image incoherent. Confusing if you will. I stick with a single theme and work from there :3
Overall i like each one of them, but with some tweaks here and there you'll get them to really pop. It reminds me of me in earlier days, the problem a lot of people have is making their render "blend" with their background. (Which is why anime characters are so easy to work with xD)
Good job man, keep it up, keep practicing and keep determined and you'll be winning SOTW contests in no time ;D
Thanks you all for the tips you have given me. They will be very helpful to me. I want to become better during time and tips from other people is the best way to become a better Photoshop user. Thanks.