Valve Time is a popular joke because of Half-Life, but if you set that aside they actually release things pretty consistently. With all the engine improvements

Valve Time is a popular joke because of Half-Life, but if you set that aside they actually release things pretty consistently. With all the engine improvements and content updates, TF2 in 2013 is only barely comparable to TF2 in 2007 in terms of gameplay, and not at all in terms of system requirements to play at high quality. And apart from that, since the Orange Box in 2007, they've released major games in 2008 (L4D), 2009 (L4D2), 2011 (Portal 2), 2012 (CS:GO), and 2013 (DOTA 2). The only year they missed was 2010, but that was the year they released the OSX ports of all the Source games. They also rolled out Linux support this year, although I imagine the transition from OSX to Ubuntu was much less difficult than from Windows to OSX.