In my opinion, Steam is a service that should be better than what it is. It has been around for more than a decade, but it is still a problematic service that simply doesn't do it's job well. It is convenient. It helps gamers do things they would have to use several other services to do. But it is heavy-handed, invasive, and can be unstable if you use it to play co-op. It is an unreliable back-up for your save files. And, if you require assistance be prepared to wait days for someone to contact you with the first automated response.
It is also a lie. People make a big deal about Steam sales - but the fact is, those sales rarely offer games for prices you can't find other places. If you pay attention to the games you want to buy, you can often easily find prices as good or better before Steam decides to put them on sale. Steam is essentially the impulse-buy capital of the gaming world (Look, I can buy this game I'll never play for $4.99!")
Yes, you can make sure Steam doesn't install games and/or update them without your permission, but if you don't know before-hand how to set it up it could be a problem. And, why would it automatically start downloading without knowing the speed of your connection anyway? That's just bad design. There are millions of gamers - most of us - that have service which is slow enough that installing by disk is much faster. Yes it is very convenient to let Steam do it, if your connection is fast enough. I personally don't install from disks anymore, I'm lucky enough to have good, fast service where I'm at (and don't get me started about how the U.S. still has terrible internet for most of it's people, about how it's politically controlled business system thwarts true capitalism and allows bad service to stay operational in much of the country), but assuming people do demonstrates a lack of understanding that I find mystifying.
All that being said, Steam IS improving. It is overall a good service, I freely admit that my dislike for it comes from the days when it was a terrible service. It is no longer terrible - and, truth be told, what piece of software you have to deal with, whether it is an operating system of any kind or something professional level, doesn't have something just weird about it? Steam is convenient, provides some nice benefits, and is mostly something that doesn't bother me when I 'm gaming. I rarely buy from Steam, I prefer Green Man Gaming or Gamestop (more because there are some nice, helpful guys that work at the one close to me than any other reason), but there may come a day that I think Steam is so good I'll support it by buying my games from Steam/Valve instead.
As far as games shipping incomplete - no. Back when all our games came on disks there weren't any patches or fixes, the games just stayed buggy. Now, developers continue to support their games after they have been released. Games are much larger than they used to be, made by much larger teams, and for those reasons alone are more prone to having problems not discovered until after they are shipped. But the biggest reason we see patches shortly after a game is released is that the majority of us have a good way to receive those patches. Not all that long ago, most gamers couldn't get a fixed game without a new disk being shipped to them. It isn't fun to have to wait another hour or two -or longer - to play a game after you finished installing it, but in my opinion that's better than being stuck with a less functional game.