I am quite impressed with your work here. The eyes are great, the lighting is fantastic, and the little touches with the bottle and the sword really pull it together. Now for some comments:
 The shadow of her back leg, right in the center on the ground, seems a little bit off. Maybe skew it more.
 The angle of the arm that is holding the sword seems slightly awkward. It probably would have been better to have her resting her arm on the armrest, possibly holding the sword by the crosstree instead of the hilt. A much more casual feel.
 The wood texturing on the throne seems...simplistic. I'm reaching here, but it seems like it's not quite gritty enough, or it's too uniform. It might be the sharp black gaps between the pieces.
 I was under the impression that the Scout-pattern legs (the original ones) were white, to match her coat. Not that important though.
On the whole, this is a very solid piece. Everything focuses the viewer's attention squarely on Blackjack's face, but there is plenty of extra detail to stare at. ALL HAIL QUEEN WHISKEY!
...Okay, only now do I find out she's not a stallion. I was similarly confused at the beginning of FoE regarding Littlepip... and at the beginning of MLP:FIM regarding Applejack... I really need to start reading "Project Horizons".
Read Fallout Equestria: Project Horizons. Those are actually cybernetic augments built by a friendly diamond dog after Blackjack got her legs blown off. Yes, the "Scout"-model front legs have griffon-style hands for added functionality.
Well, the radiation thing isn't too far off from reality. The all-blown-up part? That kinda just happens. Fallout: Equestria and its spiritual sequel FoE: Project Horizons are fine upstanding examples of the grimdark/gore genre. That being said, FoE is easily the single best fanfiction in the MLP: FiM universe, with side-fics and spinoffs numbering in the hundreds. Project Horizons is the second best, after the original FoE. I recommend that you read them both.
People who hated that it crossed over and that it was too comical for the story. I believe that it was a good break from the super serious and depressing downward spiral that is Blackjack's life. Long stories need small breaks from time to time. Besides, it led to the one time I laughed aloud at FoEH, when Morning Glory told Scotch Tape to ask Blackjack REALLY LOUDLY WHAT A HANGOVER WAS!