The "death" of Sully was really powerful for me, like others of said. As powerful as his "death" was, the reveal that he was in fact alive and completely unharmed was equally infuriating. I think most of my problem had to do with HOW they revealed it. It should have had far more emotional weight to it than "Holy crap? You're alive? Is it really you? Oh, it is, lulz. Let's go".
Perhaps they could have gone a Last Crusade route with it (if the macguffin had healing properties). Or perhaps it was just a matter of Nate getting back to Sully's body after the final fight to see that he was still (barely) alive, and the end of the story could be Nate dealing with the guilt as Sully is healing in ICU, and the could wrap up with exposition between Nathan and Elana with Nathan acknowledging his obsession and the reality of the danger it comes with. They just needed SOMETHING to keep the emotional weight and fear of consequence they kept talking about throughout the game. Sully's death showed a lot of potential for that pay off, but how they "fixed" it was incredibly weak and killed all of what they tried to do with it.
Fully agree.