If you haven't read through the "On the Special Snowflake Setting" by the irreplaceable Courtney Campbell, you should. He goes over a number of problems more eloquently than I would and I pretty much agree with every statement, so I'm not going to bother adding more.
I just want to offer some practical advice.
If you look, his examples start with "Does anybody have any feedback?" and that's a great question if your players are all comfortable with each other and have a reasonably open relationship. But not all games are like that, and not all people are like that. I've personally found that a lot of people I've ran games for have serious reservations about giving feedback for fear of "complaining" or "being negative." 
Far more effective for me than a blanket statement to the whole group is individually sought feedback. People that might not answer a call for "anybody's" feedback will almost certainly answer if you ask specifically for theirs.
A quick example of how both approaches play out for my current group:
DM: Does anybody have any feedback?
DM: ...Really, nobody has any feedback?
Joe: No, everything's good!
DM: There's really nothing you have to say? I'm completely open here, I'm looking to improve.
Steve: Well, yeah, what he said.
DM: Alright, well, see you next week, then!
Not exactly productive. But if you ask each player individually:
DM and Player A via IM
DM: So what did you think about last week's session?
Joe: Oh, it was alright. It was frustrating not being able to damage those guys, though. That one guy took like seven hits and was still alive! 
DM: Oh yeah, well, I did get a couple of lucky rolls and plus you know that kind of armor has damage resistance against your weapon type.
Player A: I guess, but still, it was frustrating, especially since they couldn't really damage me, either. You know that NPCs can also have Option X and Option Y...
Cue cooperative NPC creation theorycrafting
Or another example:
DM and Player B via IM
DM: Hey, what did you think about the session last week?
Steve: Oh yeah, it was fine.
DM: Just fine?
Steve: Yeah, I thought the story was going to be different- I created a character for Plot X and it ended up being Plot Y, and I'm not enjoying being in the jungle!
DM: What do you mean?
Steve: Well me and Player C are really urban, you know, like we're from cities and are used to grifting and stealing and partying and charming ladies and all that and that doesn't work with the jungle!
DM: Well, that's true, but you shouldn't be stuck there much longer! You did find that outpost, remember? And what did you mean about the plot thing? 
And so on...
The point is that, if you have a group like mine that won't give feedback in front of everybody, asking them in private what they're thinking about the game can get them talking.
If they still insist things are fine, you can suggest things that you're not personally happy with. Leading with a "I wish Charlotte would speak up more" or even something a bit self-deprecating, such as "I keep making the battles too easy!" or "I'm sorry the game's so slow, sometimes" can really let people know that it's ok to talk about the game and that you really are looking for criticism.
If they still insist things are fine after all that, maybe things are OK. Maybe they really are happy.
Or maybe you're such a bad GM that they don't feel like it's worth wasting their time giving you their opinion because you won't listen anyways. You're going to have to pay attention to see which it is and honestly if you've read this much, you at least have the right attitude.
: Plus some players are just shy! I have a hell of a time convincing myself that my opinions are important or valuable, especially when everybody else seems to be fine with the way things are. But sometimes you end up on a trip to Abilene...
: He'd become used to swinging his sword every turn (and indeed, built his character around it) and had a hard time thinking outside the box with another way to deal damage. He could have tripped, taunted, used the environment, or any number of other things... But in his defense, "sword attacks" had been working for him the whole time and he was just delaying while the rest of the party dealt with the archers on the flanks. I'm not sure what either of us could have done differently, knowing what we know. Each turn I was thinking "You're not getting anything done, do something else!" and he was thinking "I haven't done anything yet but this next blow could be the one- I'll just keep at it!"
: I said "roll up characters that are leaving their home for some reason- you're going to be starting on a ship travelling across the sea," and one guy said "like Morrowind?" I replied "Kinda, I guess," and I had meant just "can't go home; must go forwards" but none of them went with that angle in their backstories- 2 of them ended up on the boat by accident, 1 was a self-exiled wandering-warrior daughter of nobility, and 1 of them was an amnesiac priest looking to do good, and 1 of them was a quiet street rat running from the law. So I scrapped it, because by all of them creating characters with links to their old world they have indicated that their character's homeland is still very much important to them. It actually turns out I was right, as when I told them the cultures of this new land they all immediately decided they wanted to be one of them, and one of my players actually helped me flesh out his characters' homeland because, so we spent a very pleasant two or so hours hashing out all of that.