That is great if you have a fast, stable internet connection. Not so great for those of us who don't.
Good point, it depends on the type of game.
If I take my laptop on vacation with me and want to play Panzer Corps or somesuch turn-based game at a leisurely pace WITHOUT signing on to steam, without logging in to some random Wi-Fi...
... also I'm not a big fan of games that RELY on a central server either for authentication or matchmaking. Update servers- fine. Not having to hunt down patches is a great feature, but forcing logon to play single player is annoying. The Wargame AirLand Battle games are an example of this.