This is the main issue I have with steam, you have to start steam to play any of your games, and what's more if you don't have internet, you can't access your games. there is offline mode, but you have to activate that while being online.
every game I've bought on steam, I then promptly pirate.
Half the time steam crashes on startup, and when I did use it a few years ago, I needed to uninstall and reinstall frequently.
That said, I did play a few games I wouldn't have otherwise eg terraria and audiosurf.