Honestly, these are almost professional-quality compared to my first 3 sigs. I like how you use a larger canvas; that's my style, too. Much more room to work. You're probably going to hear from a lot of people on the first two tags that the lighting is too much. It is. Definitely tone that down, overly done lighting = focal killer. Also, on the first one, a rule I always try to remember for text placement is PUT IT NEAR THE FOCAL. 93% of the time, this will reduce any possibility of the text distracting from the focal point, because it's right next to the focal point. I see you incorporated depth, which is definitely nice, although it seems a bit overdone in the bottom two. In the hulk one, I'd suggest slightly blurring a bit of the Hulk's right arm, just to blend the render and BG. I'm liking the coloring in these pieces; I'm guessing/hoping you're making use of photo filters and gradient overlays and the sort. Finally, the biggest problem. The logo. If you're keeping it in there as a trademark, then I guess it can stay. But if it's in there purely for looks, remove it this instant. Logos = focal slayer.
Overall, I'd say very nice for your first 3 signatures, KIU!