The mirroring of the TWOK scene, down to the dialog, was entirely deliberate, but not just gratuitously. A recurring theme in both films is that, despite Nero’s incursion having created a new timeline, some nebulous concept of ‘destiny’ applies and the universe arranges for characters to come together and for key events in their lives to happen anyway – thus Kirk meets Spock Prime on Delta Vega, where Scotty conveniently happens to be holed up in a Starfleet bunker. In this vein, Kirk was always destined to meet Khan, and Kirk and Spock’s relationship would be at least partially defined by one of them dying to save the others. The execution was poorer than it could have been – as pointed out, at this point Kirk and Spock are not nearly good enough friends at this point for it to really mean anything – but you can see what they were aiming at.
On the Khan’s blood thing – it’s not some miracle cure for death. The dialog establishes that. Kirk is technically dead, yes, but not so long dead that his brain would have degenerated past the capability for repair, if his blood and oxygen supply could be restored. The conceit about Khan’s blood is that there’s something in it – whether purely a result of genetic enhancement, or nano-machines, or whatever – that helps his cells repair themselves. OK, it’s convenient, and yes, it might lead to medical breakthroughs in the JJVerse future, but it’s not like you could dig up your year-old-dead friend, shoot him up with 10cc of essence of Khan, and expect him to spring back to life as if nothing had ever happened. Neither is it suggested anywhere that Khan and his people are immortal. They may age more slowly than regular humans, or they may not – the gap between Space Seed and TWOK was relatively short (IIRC it’s supposed to be 15 years?) but Khan has definitely aged a fair bit in that film.
Yes, it’s a macguffin, but there’s nothing new about that in Abrams’ films.
There’s a plot hole a mile wide around the whole people-in-torpedoes thing. Given the damage one photon torpedo could do to a planetary surface, 72 ought to be enough to wipe out a continent, so as a captain I’d question why I was supposed to fire so many just to kill one man. But then Kirk is supposed to be a mad dog looking for revenge for the killing of Pike, his surrogate father. So maybe he’s not so logical after all. But for me, this is actually the weakest part of the plot – it’s basically just a device to explain why Khan surrenders.
I enjoyed it for what it was, a summer blockbuster action adventure romp. I’m not expecting the character depth you can get in a TV series. The previous movies didn’t have that either, and many supporting characters got short shrift there, too, but that’s a limitation of the movie format; you can’t really have a genuine ensemble cast in this format.
If it keeps Trek alive long enough that it eventually makes it back to TV, then I’m all for more from JJ and co.