I think the number one thing, at least for me, that keeps Steam so competitive is its refund policy. Devs, especially indie devs who make short games, hate it, but I don't know any other platform that has something like it.
For those unfamiliar, you can return and refund any game that you've played less than 2 hours. Now this obviously sucks for any games that are less than 2 hours in their entireity. (Maybe they need to adjust it to less than an hour?)
But for someone like who can't afford to waste money on games that they aren't going to play, this is great. I just bought a game (Phantom Doctrine) on Playstation. It was $6 which is a really good price. I'd been wanting to play it for a very long time. I was very disappointed. It's like X-Com with a spycraft theme but much worse gameplay. Played an hour and knew I'd probably never play again.
I've bought four games on Steam and returned all of them. Most because they just didn't run on my computer. The fourth one, I just didn't like very much after about ten minutes.
One thing that does suck, if you're not aware of it, is Early Access games that just get dropped. I can name half a dozen games off the top of my head that I spent good money for and the dev just dropped development halfway through or released a shitty buggy product. But I think as long as you wait at least a year to buy an Early Access game, you should be fine.