Steam is not a mac-like app, and in fact isn't even a terribly good Windows app, the DRM is very restrictive in spite of the initial impression that it isn't as restrictive as most (see below), but there's just no way to not be happy that Valve is bringing there games to us, as well as other developers. The Steam client and DRM is utterly crappy. The games are great.
One thing I dislike about the Steam client is it has a really lousy way of browsing games. It shows you 10 (or some number) of games at a time and you have to click to go to the next page. You can't just scroll through the list. Worse, if you get 6 pages in, then click on an app to read about it and then click the back arrow, you don't end up on page 6, you end up back on page 1! That's not a good way to encourage use of your application.
Also that you can't paste into the password field (or any other field) is another way to discourage purchases. It's a nuisance to buy anything with Steam.
On top of all that, Steam comes across as an attempt to be something like the Xbox, but it's DRM is more restrictive and that's highly disappointing. On the Xbox we can have multiple profiles on one Xbox, each with their own save(s) and their own sets of achievements, and if we buy a download game for it, all the profiles on that Xbox can play them. With Steam, when you buy a game it is only playable in the Profile that purchased it. For someone like myself who has two gaming kids, this makes the value of Steam seem questionable. I'm not going to buy any games on Steam that I think my kids would want to play because there's no way I'm going to buy 3 copies of it just so they can have their own achievements. That's ridiculous.
Still, Portal was free and I got it and it was great. I also own a copy of Team Fortress 2 which I bought a while back when they had it on sale for a ridiculously low price, and I'm looking forward to when they enable that on the Mac. When I can get stuff that's just for me and is super cheap, I'll buy it, but no way am I ever going to pay full price for anything on Steam - it's not worth it.