I've been using it for several years now and find it to be fun, handy, and dependable. Most complaints are unwarranted. Steam itself is free, and games available on Steam are undergoing a
Christmas sale right now until January 3rd, with Left 4 Dead 2 currently 25% off. And even when that's not going on, there are new sales weekly.
I seen a number of benefits: it's free; there's no need to find disks; you can play your games on any computer with Steam installed; you can stay connected with friends and see what they're up to; and you can keep track of achievements.
Of course, there are legitimate downsides to any online distribution software: there's no physical media for data backups; there's no ability to play online when Steam servers go down; and there's the possibility that Steam itself might go under, leaving you high and dry.
Still, you can
backup data, as well as
check file integrity and re-download if necessary should any data become corrupted. You also don't need to be hooked up to the Steam network to play alone in
Offline Mode. And the likelihood of Steam going under in the near future is very low with companies like 2K Games, Atari, Activision, NCSoft, Rockstar Games, Sony Online Entertainment, and Ubisoft jumping on board.
If you're still leery, you can buy any game from Valve Software (such as L4D2) and a few games from other developers at retail locations and
activate your copy on Steam to give it a test run. You likely won't be disappointed. This should alleviate most of your concerns and give you a stress-free way to test out Steam on your own. Check the "
Information for New Users" page if you'd like to know more.