Steam has good points and bad points. As a modder, no hacking mods for online, more like adding user made content like new characters and only modifing gameplay if it does not effect online mod (you'd be surprised how many console gamers I have to explain that to), Steam usually gives you a great service. Corrupted file and you forgot to back up this critical file? Delete it! Steam will automatically replace it next time you try to play the game. Also phsyical copies only exist for me on Steam as a way to prove ownership of my account if ever hacked. The CD's for Fallout New Vegas, The Orange Box, and a handful of other games have not left the case since I installed them the first time. Never have to worry ever again about a disk getting scrached, all that is important is the code and since that is already tied to my account all that matters is at least one code for a game survives. And as far as DRM is concerned Steam's is much less sadistic than others *cough* Maxis, Ubisoft *cough*. I remember that virus that disabled CD drives that was supposed to a anti-piracy program that automatically installed on some games from the 90s, Steam is by far not the worst step taken in anti-piracy especially since Gabe Newell himself said that piracy can be fought by giving a better service than the pirates. And great games often go on sale or go free to play for a weekend giving you two days to play the full game, not a demo, as it would be if you had bought it (not all games mind you, like the ones you could milk for all their content in a weekend). And unlike Games for Windows Live the games are not as restricted allowing more freedom from small things like custom emblems that appear on your character/army to major things mods (you had to break Windows Live to mod Fallout 3, but then again the Steam version was a bigger *****). Now on to the bad notes:
Steam, as far as I know, CANNOT be started in online mode if your internet suddenly and unexpectedly craps out. This has angered me more than once, though it doesn't happen often when it does happen it is infuriating. Also not all games can be modded on Steam, even if their non-Steam version was completely moddable. Sometimes they fix this but a lot of times they don't. Bethesda (for a short time) and Lucas Arts have been some of the worst offenders. Either most mods didn't work (due to encription in the .exe file that was illegal to change) or the game was completely incompatable with mods.
In the end people disagree on Steam because they prefer different services. Some like the features Steam brings, others hate the limitations you must put up with to enjoy those features.