I think that what it's missing is a brighter layer of highlights on the texture and raised areas - the depth of the model is somewhat lessened by the 'flat' paint job. By which I mean, the way that the whole model is painted in a similar paint scheme. If you use the same colors but with a bit of white (or off-white) added, and drybrush the edges of the different layers, I think it'll really make the whole model 'pop' a bit more.
Not to criticize your great work (and I love the way you've mixed red in with the grays on the stone!), this is just meant to be friendly and hopefully constructive advice. The project looks excellent, I think it just needs some slight tweaking.
-Alex