I miss all those old school RTS games like Total Annihilation, Command and Conquer series, Age of Empires etc. No one really makes decent RTS games now.
There are several so-called 'spiritual successors' on Steam; just spend some time reading the reviews of the official successors to find the negative reviews suggesting alternatives. One potential qualifier: http://store.steampowered.com/app/335940
I've received Grey Goo with a recent Humble Bundle, it feels very much like an old school RTS with three different factions (Starcraft-like) with a focus on base-building and resources
Also miss all the pre-bittorrent P2P clients.