Some dead trees in the spots above those netherbrick rooves would look really sick, also add terrain. Kind of funny you already showed me this hahaha
Looks a little bland? It's mainly just gray everywhere, try different textures with slabs/ other materials
As @wrightrj said, due do concentrated use of stone bricks, it looks bland in those areas, perhaps try spicing it up with black/red tones (coal block, obsidian, red stained clay etc) Can't really say much from an architectural standpoint, as it's only a frontal screenshot, might you be able to post some more from different angles?
First of all the ground on which your build stands is very flat, do some terraforming, the 2 things on the sides (are they finished) you cant leave them like that make them useful for the build, and the last but important suggestion as @wrightrj and @TrigaJoules mentioned you need to add more color and diversity to it (Not just grey). I'm sure you will make something fabulous out of it. *Thumbs up* ;D