Yup, agreed with OP, except personally I don't think they make great games anymore, and heavily use(and have used) the promise of future titles to keep people coming back while putting in seemingly next to no effort or profits into their "big" titles of their own.
Its become a commercial selling platform, not just the program they use for their own games.
Portal is great, but short, and portal 2 for me was significantly worse, easier and less daring than the original like any other series. Likewise HL1 was the best, HL2 was good but not as good for me, all the episodes I think have been complete crap, rehashed rubbish, reusing much of the same stuff, same area's, same feel, nothing new, overpriced and way too short and years between small games without much new content.
The only reason people have complained less is... they're only making one or two series worse because they only have one or two.
Is steam fantastic, no, its a basic shop and game launching client, it offers me no more or less functionality than any other app that does the same crap for me. As said in the OP, they keep offering you stuff that is a great price... and humans in general(me included) hate passing up a good deal just in case, however I haven't been sucked into the Steam experience of spending on stuff I'll never play. There are guys who bang on about steam sales who also say they have 100's of games they've never played, never will play, never really wanted to play. I'd prefer to pay £30 on a game I want than 20p each for 100 games I don't want to play JUSt because they are cheap and I might eventually open one of them.
Steam suck on pricing for stuff you actually want, offer nothing no one else doesn't, spends a lot of time and effort getting you to buy stuff you don't really want and spends seemingly very little of its vast profits actually making games, and not making great games.
In terms of being a good platform for indie's to get their games up.... I honestly don't know if thats true, it is, lots of people use it and people can put their games on it, but I have no idea if they make much from each sale, if Valve are good, or have become a giant and take most of the profits.
I see nothing brilliant about Steam, origin, Uplay or anything else, nor anything particularly bad with them, the love for steam I don't get, its an application, its a list of short cuts, you can put a list of shortcuts to all your games in a folder and have identical "all my games are here" functionality people keep banging on about.
Its like people think shortcuts and arranging all your game ones in one list is... magic? I find how much people like a list of shortcuts so valuable, but thats just me.
If they aren't charging indie game makers through the teeth for each sale, good for them, but ultimately I see Valve as a massively profitable retailer... who very occasionally release a game.