It's funny...you're the second person in a row in my comments, who did an Odo drawing that I complimented, who said the exact same thing about Odo's face being deceptively simple but in fact really tough to draw!
I think maybe it's hard to draw because it's so simplified. With an ordinary face there's some forgiveness in all the lines that blur together, but he's just a few clean geometric shapes so there's not much room for forgiveness.
I had to look up photo ref but they did have such cool architectural shapes on the station.
I used to have a friend that worked almost exclusively in ball point pen, just amazing shading and detail, so I learned the technique from him. I've done bigger and better pieces, honestly, but not in years so they're buried way back in the gallery here.