I received this message from a friend recently, read it yesterday, and after getting set up I spent quite awhile playing it last night. Haven't seen anything family unfriendly as yet (and I am on level 15 of 19). You have to download the Steam browser to get it, but this is also free AND they have some other free games once you do. Steam has an excellent rep on the net, so that part doesn't concern me. btw Portal isn't really a shooter. You only 'shoot' where your portal goes on the wall or floor, and knock over a robot or two. This video explains, though its a lot more hectic-looking than anything I have seen in Portal yet ;-)
EDIT:: Got to level 16 (finally) and it suddenly got rougher. You have to avoid these robots..and when you don't you see your character's blood splattered on the walls :( So...to level 15 its pretty much kid safe.
The other free games are listed here: There's a racing game and a real-time strategy thingy, and a version of the casual classic, Peggle. Please note that while the usual versions of Peggle are safe for all ages, the free 'Extreme Peggle' Steam offers has 'scary monster' graphics added. IMHO the worst is the opening scene with something apparently trying to eat the unicorn's head. Gave me an extra grin given my recent blog post....
You will notice a mention of Nvidia & ATI card games on the post...both get the same freebies aside from Portal...which used to give half of the game only to Nvidia people.
If you have an NVidia graphics card, you might want to pick up your Nvidia special first if you care about the Half Life 2 episodes. The current free Portal promotion seems to be making things a little more complicated for some folks.
First impressions are that most of Steam's free games are PG-ish, and/or guy-centric...but I felt Portal was worth the trouble. It really is a fun thinking game. :-D