First I want to say, overall, great job! This picture looks wonderful, and is one of the subjects that I really enjoy, that being super heroines being paired with villains.
First, the positives:
Powergirl looks amazing. You did an even better job with her this time around than on your last Powergirl with Doomsday picture. Her boobs are much more 'Powergirl-sized' in this picture, too. So it is more on-model, which I like. I like when characters are drawn closer to on-model, like here. For instance, if someone drew Kitty Pride with huge, Powergirl-sized boobs, I would NOT like that, because it doesn't look like the character. I think you really captured Powergirl's 'look' in this picture.
The colors are really, really good. Well done on that.
Doomsday's arms, hands, and bone-stuctures are really well done.
Now for the negatives:
Powergirl's neck is to long.
Doomsday's head is to small. His body is also to small, but his head is really small.
About the scenario, which I really do love, but I don't understand the need for her to have on Kryptonite shackles. Doomsday is a powerful enough villain to just be able to over-power her, so it may have been fun to have her arms be free, trying to struggle against him, but failing. If you had paired her with a physically less-powerful villain, then I think that the Kryptonite would have made sense. This isn't a criticism of the art, but the scenario.
Based on the picture at your blog:
It kind of looks like Doomday's dick is growing out of the side of his leg.
Also, and this is just regarding my personal tastes, I would have liked it if Powergirl had had a small triangular patch of pubic hair right above her pussy, pointing down to it. Not a huge bush, but a tidy one. Though I know a lot of people like the fully bald look.
Okay, overall, the picture is really great. I love the drawing, the coloring, and the subject. Think it is even better than your last Powergirl with Doomsday drawing, and I really liked that last one, too.
I really hope you do more art based around heroine with villain pairings.
Thank you for posting this picture for us to enjoy.