I drift in and out of DF - I'll play it to death for a few months, then get distracted by shiny graphics or a new expansion for Crusader Kings. Then after a few months, mainstream games stop satisfying me with their shallow systems and their crisp, accessible UIs that just won't give me the information I want. Then, before you know it, I'm back on this forum, laughing at other people's stories and getting inspired to dive back in.
You sound like you might be struggling to find the Fun, so I'd advise-
- If you want more things to do, grab some mods. There's tons of additions or total conversions for the last version of DF. The Masterwork mod comes highly recommended for flooding you with different races to play and tons of new toys.
- If you want more fighting / hideous deathtrap use, try the last version, again possibly with mods. I've not tried the new version yet (was stuck on a long-term fort from the previous version last I played), but it sounds to have a lot less invasions. There's also mods, such as the Fortress Defense one, to add even more invading races.
- If efficient design is your thing - it's certainly one of the main uses of my time in DF - look into the manifold joys of minecarts. Why have your dorfs carry things around like losers when you can have a hideously complex rail system set up, dropping everything exactly where it'll be needed next? Why not automate everything except the actual loading of the carts? (Disclaimer: May not actually increase efficiency. May cause injury, dismemberment, and/or death. May adsorb ungodly amounts of time.)
- Lastly, try to think like a dwarf. Don't just put corridors because people need to get places - think about how it'll look, how it'll feel. Make entrances and halls several levels high, line corridors with statues, aim for something that says "grandeur" as well as utilitarianism. I find this helps me think of my forts as real, living places that I have a connection to, as well as giving me reasons to design things differently each time.
Hope that all helps