Part of the success of the movie I also think comes from director and co-writer Guillermo del Toro. I have seen and enjoyed his movies before and had confidence that he could pull this movie off. Del Toro managed to create a movie that it made it believable we could have a world where giant monsters could be fighting giant robots. He created characters that were believable enough. But while they could use possibly a little more character development he gives you enough for the action movie that it is. With that said, he gave us characters that are different and diverse enough from each other to help the movie. The other part I wish we had more of in the movie is possibly a little bit more mythology or backstory of the monsters, but not having that did not heavily take away enjoyment of the movie.
Overall for me, Pacific Rim, was different enough and great fun seeing giant monsters fighting against giant robots. The monsters and the robots were the real stars of the movie since there was not any real A-list stars in it and that worked just fine, since it allowed the movie to showcase them even more. Finally as some who often enjoys the film scores I quite enjoyed the score by Ramin Djawadi.