If you liked the first one, you'll probably like this one. More giant robots, more giant creatures, more loose interpretations of science. Still, it was a fun movie. I probably even liked it a smidge more than the first one. You have to suspend pretty much all of your disbelief for it, but that's to be expected in a movie like this.
Pacific Rim: Uprising takes place in the distant aftermath of the first movie. Things have been peaceful, but they're rebuilding in case the bad guys decide to rumble again. They're looking for good pilots and good recruits and are apparently so desperate for them, they'll take any criminal showing promise. Of course, this makes little sense as the whole world would be sending their top people constantly for this, but, again... if you saw the first one, you were prepared to have to turn off your brain. Well, the son of the savior of the world has to come in from his criminal ways to save the day. He brings with him someone that built her own robot from spare parts! They train, they fail, but then more monsters come and they have to save the day, so they suit up!
I think the makers of these movies underestimate the population of the world. In the first movie, giant monsters destroy cities and the news report says that tens of thousands of people died. That's multiple cities walked through by giant monsters. Millions would have died. And it makes sense, then, with the much-lower populations that it would be tough to find recruits. Since this is set in the future, maybe people are just having far fewer babies (as is really happening). Maybe the populations ARE dwindling, making this movie more plausible. Maybe it's saying that we need to make more people before the giant monsters come, so we'll be ready! Or maybe it's just a silly popcorn movie that is kinda fun to watch with your brain shut down. Yeah, probably that last one.