I think the modern (and unfortunate) trend in game design is to tune the default/normal difficulties so that players can ignore/underutilize many gameplay mechanics yet still succeed; it isn't until you turn up the difficulty that you're really required to play many games as they were designed.
In the case of BioShock Infinite, I think this is definitely the case. I played through the game the first time on Hard and had major issues getting past the same encounters that many people have complained about. It wasn't until the first Siren battle that I had my "Aha!" breakthrough. I finally decided to rethink my approach after 2 hours of trying (I'm stubborn) and discovered that the encounter was a trivial 15 second affair with the Hand Cannon and Murder of Crows w/Crow Traps Aid. This approach didn't work for the second encounter with Lady Comstock (the minions in the bank are immune to crows), so I had to come up with a different strategy (in this case, Shotgun + Charge w/Charge Aid). Once I had gotten it into my mind that I could be very creative (and non-traditional, in FPS terms) with my gameplay, I started having a lot more fun. In fact, I liked the Shotgun + Charge combo so much, I further explored that style of play for my 1999 Mode play through, where I luckily found all the right gear:
- Hat: Electric Punch (70% chance for melee to stun for 4 seconds)
- Vest: Blood to Salt (40% chance for salts on kill)
- Pants: Brittle Skinned (melee targets take 2x damage for 5 seconds)
- Boots: Overkill (killing with excessive damage stuns nearby enemies)
Since Charge and skyline/skyhook attacks both count as melee attacks, this was a lot of fun and allowed one set of gear to work in basically all situations. I upgraded Charge with Charge Aid (grants invulnerability and starts recharging shields immediately after Charge) and used Return to Sender heavily in the late game. This equipment/vigor combo totally changed the pace of combat for me. My gameplay loop went from the traditional shooter tropes (popping in and out of cover, waiting for my shields to recharge, backpedaling frantically away from heavies) to something that felt quite similar to the Vanguard class from Mass Effect (rush in, kill before the invulnerability runs out, chain stun, repeat until everything is dead).
After my first time through, I considered the biggest difficulty spikes to be the Lady Comstock encounters and some of the big, chaotic battle arena sequences. After playing BioShock Infinite a second time, however, I think the hardest part of the game is the first battle sequence, right after the raffle, where you have to deal with two turrets and several armed guards with no shields and nothing but the pistol and the expensive version of Possession. It's at this point that you have nothing but the most basic tools to work with and the game feels like most any other shooter.
I think you could fault the game a bit for not encouraging the creative approach to gameplay more, but I have to admit that I was pretty embarrassed at myself for playing a BioShock game like a traditional shooter to begin with. Considering how much time I spent playing the previous games, I should have learned my lesson the first two times.
It's interesting that opinions on Hard/1999 seem to vacillate between "too hard" and "kind of easy", particularly because the suggested play styles of the people in the "easy" camp vary so greatly. I think that's a testament to the depth of the systems that there are so many ways to succeed, but I think one of BioShock Infinite's flaws is that you can get away with old-school FPSing for so long. Many games have early gear/skill check sequences (ie: how they teach you to use Possession) to introduce you to certain ideas; I can't help but think that this game could have benefitted from some kind of "creative problem solving check" to get you in the right mindset.