One simple thing is all I ask of even the most cheesy of movies, please keep me in the world of the movie. Once I am jerked out of the movie's world then my perception and judgement of the movie becomes more critical.
With del Toro's new movie Pacific Rim I was jerked out from the onset. When in the opening a kaiju is simply defined as a giant beast. Under this loose interpretation King Kong and the dinosaur from The Beast from 20,000 Fathoms are kaiju not just Gojira, Rodan, Gamera, and King Ghidorrah to name a few.
Another problem is making connections of scenes from this movie to other movies. Riley and Mori remind me of Kodai and Yoko from Space Battleship Yamato. The brash Australian Jaeger pilot reminds me of Iceman from Top Gun. The Level Four kaiju dragging Gipsy Danger on the ground and carrying it into the air, too many skirmishes between Gojira and Rodan or King Ghiddorah. When Gipsy Danger deploys it's sword, it will be hard not to think of Ivy from Soul Caliber and her sword. The sub-sea rift is either inspired by X The Unknown or since we are talking an inter-dimensional rift then perhaps Battle Fairy Yukikaze. The transport of the Jaegers by airlift and how the pilots synchronize reminds me of Neon Genesis Evangelion. Once you see the ending you will go that's almost Independence Day.
The reduced science team is the most annoying thing in the movie. Which is saying something since Ron Perlman is playing the guy who runs a black market selling kaiju parts. One part of the team is this cliched crippled stiff upper lift British boffin, all he was missing was a pipe. The other one the boffin called a 'kaiju groupie.' Think of Rick Moranis' character in Ghostbusters but loves playing with the guts of alien creatures and getting tattoos of them put on his body. At one point the boffin is madly playing with his chalkboards before the Jaeger commander while the groupie was sitting just a few feet away without any protective gear tossing kaiju entrails on the floor. At a guess they are supposed to be a bit of comic relief, but they are also the science team. They might be a split version of Brent Spiner's scientist character from Independence Day. The British one is a far cry from Dean Jagger's Dr. Royston from X The Unknown or Prof. Quatermass from The Creeping Unknown.
Which brings me to another problem with this movie. Earth has tried to seal the undersea rift before and has failed. And until the science team rushes to Shatterdome to give the Jaegers the critical information they need to travel the rift, it seems they were just going to do the same thing they have tried before and failed. That sounds too much like insanity and suicide all rolled into one though it could also be called a plan of desperation - a kamikaze move.
I will mention one other thing that bugged me in this movie and give it a rest. Gipsy Danger is fighting a kaiju in Hong Kong that spits acid. Audience goers have seen this acid partially dissolve another Jaeger and instantly dissolve the facade of a skyscraper. So when Gipsy Danger grapples with the kaiju and Riley reaches into the mouth and rips its tongue out without dissolving Gipsy Danger's hand, it is another moment of being jerked out of the movie by a lack of internal consistency.
Overall I would grade it as a B movie.