One of the things I see on occasion in discussions about Fate is how the game comes across as unchallenging. Throw a whole bunch of stacked modifiers at a roll and wablam! you just got a total of +8 and wind up blowing away that measly 2 passive resistance. It's sometimes described as taking the tension or suspense out of the game.
Usually when I read these, for some reason I think of the one guy who spends all of his time combing through the rules and sourcebooks to create a perfect build. I had one of these once - he could zero in on the exact combination of ability, skill and modifiers that essentially made his character unbeatable when he had a sword in his hand. In the right hands, it's great. In the wrong hands (or with the wrong intent) it can really bork up a game.
But in a game like Fate I can see how it would deflate that kind of player. At first glance, there's not a lot of fiddly bits that can be used to tweak a character out. They can just put down an aspect, Master Swordsman of the Wablam School, take Fighting +4, pick some stunts and they're done. It doesn't feel mechanically beefy to simply state that you're a master swordsman. The mechanical bonuses are the same as someone who has the aspect Deadly With a Butterknife. On top of that, the PC may not even be in danger of dying once the dice do come out. So everything is lollipops and unicorns, and everyone lives happily ever after, right?
Well, not exactly. Because oftentimes what's missing from this mix (and their arguments against the game feeling unchallenging or bland) are compels. On occasion, I've seen compels actively dismissed. Yet compels are the GM's way of throwing a wrench in the gears. They serve the role of critical misses, fumbles, whiffs, tactical errors, and all manner of other "challenging" things that happen in "those other games". Sure, the player gets a Fate Point in return - but as the GM you shouldn't worry about that so much. What you should worry about is if the players are feeling sufficiently challenged throughout the game. How to time a compel to ratchet things up a bit. When not to compel.
It feels like a completely different paradigm than running in a system where the modifiers are stacked against the players instead of for them, or it's completely on a bad roll or lack of modifiers which creates a bad situation the PCs have to deal with. But it's not - most seasoned GMs have a good feel for when a hornet's nest needs to be kicked (and not a small number probably fudge things around to make it happen, whether they'd admit it or not). Even people that don't have as much experience likely have some sense of pacing from books, television shows and movies are timed to know when to put the screws to the players.
In the end, it isn't so much that Fate Core lacks certain things that other rpgs have, or is fundamentally different in some magical way from other rpgs. It's just that sometimes it takes looking at it from a skewed angle to realize how to get the same end result from a slightly different toolset.