You want some brutally honest input I honestly think what you have is real good, your character is probably one of the most original ones here.
Now this is what I would do next to the texture, once you have got the base muscle structure down, (which you have done very nicely), the next thing I would do is add some high frequency noise to the map.
When I see you character he reminds me of an old Asian man, like the Siamese twins Feng and Eng. So some details I would add would be: liver spots / age spots/ suns spots (they are all the same) some subtle noise on the base color layer of the skin, since old men dont have very smooth skin I would add a some color variation to the skin overall, by adding some grunge to it, not too much DONT make him look like he needs a bath, just some darker variations on the base skin color
a render cloud layer may be all it needs (set to some blending mode)
all just very subtlety. Also some stains on the pants would be nice. That would make it pop
One thing to note about using a cloud layer or slapping a grunge map over the whole thing is that it will make your seams very obvious, an easy way to solve that with, out any plugins, would be to fade it / erase it out to nothing close to the seams.
I dont mean to tell you how to do your work, it just seemed to me like with the brutally honest input comment you were sick of just getting complements and wanted some advice
so that was my 2 cents on what I would do, but thats just how I would do it, and I am not you.
I like the wrinkles you have on the face, nice detail
that sort of thing is what I am talking about.
I would also consider splitting your map up into 2 textures
you will have more room for detail if you scale up everything and put them on 2 maps
but you are pretty far along for that now.