I see that a lot of people had trouble with the Siren fights. Here's how I did it, and it was pretty easy
When the Siren goes to spawn her lackeys, she'll usually summon them in a big cluster while floating over them. As soon as they spawn, hit the lackeys with Bucking Bronco, but don't bother shooting them; the Bucking Bronco is just to keep them in the air and out of your way. With them floating, you're free to open fire on the Siren for a short time (the shotgun worked very well). Bucking Bronco is a very cheap Vigor, so you shouldn't have any trouble if the fight drags on a little. It also helps if you have the upgrade that increases the time that they're kept floating.
OT: As for my complaints, I actually have very few. I would have rather had a full weapon-wheel rather than a two-weapon limit, but I did like how it occasionally forced me to improvise when ammo got low. While perfectly serviceable, I also found the weapons to be rather bland in comparison to the arsenals of Bioshock 1 & 2, especially since there's no longer any visual changes to show that you're weapon has been upgraded.
I really don't have any big complaints with the story. The ending was a little confusing at first, but I think I've got it now, and now that I do, I actually quite like it. Elizabeth's emotional changes also seem pretty abrupt, but the story is paced so well that it's a very minor issue.
My biggest issue is actually with the Vigors. Sure, they were cool, but it often didn't feel like I needed to use them very much. In the first Bioshock, I was frantically switching between plasmids and weapons; my lightning bolt was as crucial to my survival as my revolver. In Infinite, it felt more like "Oh yeah, I remember, I can throw fire. That would be kind of cool, I guess. Might as well do that for once", rather than using them out of actual need. Of course, there are exceptions, such as the Siren scenario I mentioned above, but for the most part, I didn't need them all that much. And in combat arenas when I did need to use them more frequently, I only ever needed to rely on one or two. I also didn't like that the charged version for most of them was "set trap", especially when the Murder of Crows upgraded trap pretty much renders the rest of the traps obsolete.
Despite how much I typed, I really do love the game. Just not quite as much as I liked Bioshock 1. Frankly, it would take A LOT for a game to reach that level, and I admire how close Infinite came to that.