The big con is the DRM, and of course GOG.com is the obvious alternative if that's an issue.
That said, even though I care a lot about DRM on many other forms of media, I'm among those who have decided to just take the bitter pill when it comes to Steam.
I will say that Steam tracking your gameplay is more of a PRO than a CON to me. I like being able to get statistics on how many hours I've played which games, and being able to see those statistics (if they choose to share them) for my friends. I also like my friends being able to see what I'm playing and being able to see what they're playing. It's fun and social. And Steam's ability to display a friend's game list and filter it down to what products you have in common is genius.
Things that I think you didn't list which are also important to me for Steam:
I will admit that the biggest feature, though, for me, is probably the sales. I don't buy anything straight-up on Steam anymore, or at least, I do so only rarely. (I think I actually bought Elite : Dangerous + Horizons at the flat-out non-sale price.) Most of the time if I want a game I wishlist it, and I buy games in response to them going on sale for >50% off, which Steam notifies me of if they're in my wish list. (Well, it notifies me if they're discounted any amount, but I only pull the trigger if it's >50%, usually.)
Overall, I'm very happy with Steam. I own (checking...) 286 games on it, so clearly I'm sold on the platform. I do also maintain a GOG account (with 57 games), though. Buying direct is kind of the lowest echelon for me, if only because I've gotten to the point that I launch Steam or GOG when I want to play a game, so games installed outside of those are probably going to be "out of sight, out of mind" for me after a fairly short while. I have Magic: The Gathering: Arena: How Many Subtitles Can One Game Have as a standalone, and I just genuinely never think to launch it. Same thing for games where I have to launch platform-specific or vendor-specific portals.
That said, even though I care a lot about DRM on many other forms of media, I'm among those who have decided to just take the bitter pill when it comes to Steam.
I will say that Steam tracking your gameplay is more of a PRO than a CON to me. I like being able to get statistics on how many hours I've played which games, and being able to see those statistics (if they choose to share them) for my friends. I also like my friends being able to see what I'm playing and being able to see what they're playing. It's fun and social. And Steam's ability to display a friend's game list and filter it down to what products you have in common is genius.
Things that I think you didn't list which are also important to me for Steam:
- Cloud saves mean I can uninstall a game, reinstall it on a different computer or after formatting my hard drive, etc., and pick up from where I left off with no hassle or effort taken to worry about maintaining or transferring my save files [important note: not all Steam games are cloud-save enabled, but that number seems to be increasing]. I can even play the same game on multiple different machines and continue with my save on whichever computer I happen to be using at the time. (This can be super handy if you have both a laptop and a desktop, for example.)
- Steam serves as a good catalogue of my games. To be honest, I tend to forget about games that I have bought if they're not on either Steam or GOG, especially if I've uninstalled them temporarily. But if they're in one of those databases, then I can go to my games list and see, "Oh hey, that's right, I own that, let's play that a bit."
- Reviews, Curators, updates on what my friends are playing, and Steam's built in recommendations engine are actually quite good at exposing me to new games I might like that I wouldn't otherwise have heard of, especially from indie developers
- Normalizing features like voice chat, screenshots, gamecasting, multiplayer game launching and invitations, etc., into a super-layer rather than making each game implement these features independently makes a lot of sense, and means that a lot of smaller games that might not have these features at all otherwise gain them
- The wishlist and gifting services have been downright invaluable to me -- in the age of digital content, one of the hardest things has become giving gifts. Most ebook and audiobook stores don't let you gift individual books, relying instead on you giving the person gift cards. Streaming music and video services make the idea of gifting specific albums or movies kind of irrelevant. But Steam, assuming you and the person in question both have a Steam account, makes it trivial to look at someone's wish list and gift them a game from it. For my game-loving friends, I use that feature a LOT.
I will admit that the biggest feature, though, for me, is probably the sales. I don't buy anything straight-up on Steam anymore, or at least, I do so only rarely. (I think I actually bought Elite : Dangerous + Horizons at the flat-out non-sale price.) Most of the time if I want a game I wishlist it, and I buy games in response to them going on sale for >50% off, which Steam notifies me of if they're in my wish list. (Well, it notifies me if they're discounted any amount, but I only pull the trigger if it's >50%, usually.)
Overall, I'm very happy with Steam. I own (checking...) 286 games on it, so clearly I'm sold on the platform. I do also maintain a GOG account (with 57 games), though. Buying direct is kind of the lowest echelon for me, if only because I've gotten to the point that I launch Steam or GOG when I want to play a game, so games installed outside of those are probably going to be "out of sight, out of mind" for me after a fairly short while. I have Magic: The Gathering: Arena: How Many Subtitles Can One Game Have as a standalone, and I just genuinely never think to launch it. Same thing for games where I have to launch platform-specific or vendor-specific portals.