Wow, that's some wicked improvement! Nice job, you've come a long way in 4 years.
I like this current design and I think the variation in the scales is working really well for it. The only real crit I can offer is that it doesn't seem to fit with the background. I'd say you need bluer shadows to get a more unified look going. Also, some parts like the bottom of the base of the tail seem to have too much light on them. Highlights there would be better in an environment where there's a lot of reflected light coming from below, but under water the light would dissipate well before it had the chance to bounce back up!
If you keep improving like you have since 2011 there's no doubt in my mind that the next time you draw this dragon it's going to look absolutely stunning.