steam is just like any other drm system for your games. it phone home and prevents you from playing without a connection to the mothership.

they just have saner fallback times than other ill talked solutions from EA. but besides its pretty eyes, its the same virus.

good luck running online games as root.

I once bought and downloaded SuperHexagon on Steam but didn't have the time to test it at home. Later on the train (I'm commuting for two hours a day) I wanted to test it. Sadly I wasn't allowed without a internet connection which was really annoying.

Sometimes the game executable doesn't actually require you to be online the first time you launch it, even though Steam does. If you launch the binary from Windows explorer, there's a chance it'll work.

Only for games that require Steam. A game bought through Steam does not necessarily require Steam. Europa Universalis III can be run without Steam running. Europa Universalis IV only requires Steam to be run once (and once for every DLC you buy, in order to activate it).

These settings are up to the game developer themselves. You are right about the offline mode, but it does not apply to all games.

Running the game and installing it aren't the same thing. Some Steam can can be probably trivially copied (the game directory), and are backup-able that way, but you never know which ones, and which require more steps for installation. Steam also doesn't mark any such details on the games before you buy them.