Love the Batman VS. Scarecrow image; pretty graphically stunning.
Hulks smashin' hand isn't very well defined which doesn't work too well in vector. Looks kinda blobish :/
And I don't think the mix of digital paint and pencil works very well in the last piece.
I like your style! The first and 2nd are the strongest IMO. I think there's some wonky anatomy/perspective going on in the hulk piece, especially along the deltoids, clavicles, pectoralis and trapezius. His lower right leg also seems curved "inwards". Finally, he seems happy as a child, not raging like a hulk! . Redhood's face is quite manly.