Well, of the download services it's the best and least restricitve by miles.
The pricing is good and the unlimited installs on unlimited computers is better than any disc based DRM so far, even if Steam is essentially DRM. The community system works well enough and the auto updates are very helpful.
But it's by no means perfect, the option to back up games to a DVD(s) would be nice, similarly if your account gets hacked Valve are less than helpful. If it gets hacked multiple times they just delete it, games, stats and all, I suppose the argument is you should have been more careful with your login details but it's still a *****.
Having said that, compare it to EA's service, where you pay for a game just for it all to tell you you can't have it, then have EA support tell you to fuck off because you don't have a disc or CD key to quote. Compared to that it's the nuts.