Counter Strike is regarded one of the best FPS games out there, 1.6 (the original) is really cheap - £5 or something - so you can use that as a "demo" for Counter Strike Source.
If you do that, you have to remember people have been playing for years and you won't be as good as people until you play it for a while and practice.
It is true that Source is a lot better looking and modern than 1.6, but 1.6 still just owns the Source. Source is so much more boring in comparison.
Usually on LAN's with my friends we don't even bother with the Source, 1.6 is a lot more of an entertainment, we only played Source when it was new and felt like it.
I would recommend 1.6 over Source, they both look old by now, but as an entertaining multiplay-FPS the 1.6 is way much better I think.
You could try out Wolfenstein Enemy Territory That is a very fun game and it is absolutely free. Played it loads and loads a couple of years back. Then I discovered LFS.
I believe the Master Server for the beta was disabled when the final version was released a couple of weeks ago...so although he MIGHT be able to play on a LAN, he wont get online very easily...that is, if they are still giving out keys, which I very much doubt.
You should've asked that before, you just missed Left 4 Dead demo. It was amazing and incredible for playing, but since the full one is out there's no more demo Anyway I think it's worth it the full game.
But if you want a full game from Valve completely for free, then you just have to own a nVidia graphics card or a ATi one: Half-Life 2 Deathmatch (FPS, online, pretty much populated) nVidia | ATi
Note: you'll get about 4 other games for free in this pack, it's just that the others are not online, so you can choose if you're going to install all of them or just HL2 Deathmatch.
Anyway I hope you find the game you're looking for.
And CSCZ owns them all CZ is a little better looking and i think its better then 1.6 i just get noobed in the head whenever i play 1.6 now days and source is full of excited children
It only sucks if you want dazzling gfx over super fun gameplay. I haven't actually played an FPS more fun than RTCW:ET. There is just so much to do and so much fun to be had. The gfx are poor compared to this generation of FPS games but I am yet to find a game from this generation that is as fun. Been ages since I played it because in my spare time I am on LFS but if I had the time I would certainly install it again. I have got CSS but there is not much to do really. Just spawn, buy, shoot, die. In Enemy Territory there is so much more to do so you don't end up getting bored after 5 minutes. It's quite an amusing game. I have Battlefield 2 and in some ways I prefer Enemy Territory to that aswell. Battlefield 2 is the better game but Enemy Territory is just a simple pick up and play kind of game with plenty to do to keep you entertained.
yeah you can do lots of things in it, i always went trickjumping and that was actually quite fun.
lots of friends were playing it also, but suddenly they all stopped playing and so did i