I went deep sea fishing in the Florida Keys on Sunday. We were allowed to bring what we caught to this local restaurant and they prepared it for us. We had the greatest blackened grouper that I've ever tasted -- I need to learn to cook like this.
I did something similar in Key West a couple years ago. We caught a lot of snapper and one grouper. Took all the filets to Hogfish Tavern, and they cooked them 3 ways for us (fried, blackened, sauteed with herbs). Was freaking incredible.
I bet the amazing freshness of the fish, over any particular blackening spice or cooking technique, was the main driver behind the phenomenal results. Certainly helps to know how to cook fish properly, but using a fish you pulled out of the ocean just hours before is the biggest thing.