Came in to say that I mostly agree with SenorBeef - Valve is largely great because they’re a ‘nice’ publisher. That’s a reason to like them in itself, but it also leads to their games being better.
In a maybe-separate-or-maybe-related point, it is illustrative to listen to some of the developer commentary in the Left 4 Dead games or Portal (maybe others - those are the ones I’ve listened to though). For instance, did you know that in Left 4 Dead there used to be a special type of zombie called (I think) a Screamer? The idea was you’d see it and it’d suddenly run away, and if you didn’t manage to kill it in a certain amount of time, it’d start screaming really loudly and attract the horde. So the moment you spotted a screamer, the game’s focus shifted to killing the screamer at all costs. The zombie itself was a former person in a straitjacket. Sounds like a pretty neat idea to me, especially given their notions that special infected should suddenly change how you play (Boomers and Witches break the ‘shoot anything that moves’ rule, for instance, and Spitters and Chargers break the ‘stick close to your teammates’ rule). But, they implemented the Screamer, apparently including at least concept art and perhaps in-game art, tweaked it a bit for maximum fun, and… found that it wasn’t much fun. It was too hard to see a screamer as separate from the regular zombies, so encountering one was a bit of a crapshoot. So they did something that a lot of developers wouldn’t do - they got rid of it. All that effort, all those developer hours, gone! Partly because their designers understand that less is more. But I would argue that it’s because as publishers, they aren’t dicks. Often in that situation, a developer would know that a feature sucks, but they can’t (or feel that they can’t) go to their publisher and say ‘hey you know that month of work that you funded? We’re cutting it’. So they leave it in, and perhaps even spend more months of work polishing it, and their game is worse for it. But Valve has the finances, the clout, and the philosophy that allows it to make the right decision for their games independent of concerns like that. I think that’s a big part of what makes their games so consistently good.
(The commentary reveals another reason - they grasp that loads and loads of playtesting is highly valuable - but they’re not really the only company to have cottoned onto that fact.)