Latest one.

[Mr. Positive]

This one took me about an hour to make, not too long but I like it.
CnC please.

[Fork]

A bit to monotone, Not liking the lighting at the end of the guitar, The guy looks all strechty, Not like the c4D placement and the fact the text is hidden behind it. Try using some gradient maps and setting them on different settings to get nice colors and blending.
Not really feeling this one.

[Garis]

Agree with FORK. ;]

Read some tutorials here.
They are awesome ;]

[Papa]

Lens flare isn't a good way to create lighting. Instead of using it do the following:

Black layer
set it to linear dodge
Get out a 100 px paint brush, o % hardness and 80% opacity. brush once in the color of your liking where the lihtsource should be.
Finally if you want to go a step further you can duplicate that layer and gaussian blur it to add color to the sig and give the lighting a really glowy effect.

I think you need to work on your blending. I can see the guitarist very easily and he seems to be very pasted on. WOrk on c4d's and clipping mask and smudging to get him blended easier.