Just to begin I want to say that this is a fantastic piece. I play the Undead a lot and I know what their models look like off the top of my head as a result. There are a few nit-picky things that I can see in this so I'm just going to point those out for you.
The ground is the thing I like the least. I can't tell if it's supposed to be the edge of a cliff of just something we can't see very well. I can see a rocky texture (which was done very well by the way) but just the way it's placed there looks odd and draws my attention away from the very epic rogue above.
The claws on the toes are a bit off. On the forwards facing foot they look like they're pointing off into space rather than touching the ground. On the foot pointing away the toes look to be a bit too short and don't meet the ground like they should.
The pole of the flag doesn't meet the ground all the way. Again this is just a nit-picky little thing. It doesn't take away from the original drawing and you really have to look hard to notice it.
One thing however that does really bug me about the flag is the bit that's ripped. The rips look very smooth. I would imagine the rips in the flag to look something more like the rips in the pants.
The bones in the legs are fantastically drawn. I love the shading on all the bones. However the bones in the arms don't even look like bones at all from the shape. By the shading and from playing the game and knowing what they are I can tell that they are bones. However the way their shaped makes them look more like the skin of the arms.
I don't like the fingers on the hand that isn't hidden by his leg. They're too skininy if you're going to do it like that. As well in the game the undead race doesn't have any skin on the top half of their fingers, just bone-claws. Much like their toes. I'm assuming you know this already. I'm simply mentioning what I'm comparing it to.
I LOVE the rips in the clothes. What you did with them - keep it up! They look fantastic and real! It's a subtle touch but it really does amazing things for the whole.
The forward ribs look like they were shaded a bit too darkly. The other two aren't shaded as dark. In fact that dark of shading only appears in one other place on the bones and in this particular spot looks out of place.
The head is AMAZING! You got the glow from the eyes PERFECTLY! It is amazing. Don't you ever stop doing that EVER!
The shading is lacking on the shoulder pads. It looks like it is because they're closer to the light source but it makes them look more cartoony than the rest of the image and out of place because of it.
The background is fantastic! It's minimalistic but it really does the trick! I can see the effort you went through to shade the background with a rocky-texture too and it's really good!
I love the handles of the daggers as well. The skull shape isn't very defined but I doubt you could define them better when they're so tiny. The glow effects on the dagger that I CAN see is amazing. You're very good at the glow. The shine on the dagger itself is fantastic. Though it makes me question where the main light source is. There doesn't seem to be a main one and the highlights reflect that. (Hah, bad pun.)