SPOILER FREE!
Is Pacific Rim Uprising worth seeing in the theater? To answer that you have to ask yourself what are you looking for from it? If you want cool monster fights and giant robots brawling then you will not be disappointed. If however, you are looking for an engaging story or memorable characters then you will not be very happy. So I would say if you love seeing giant things fight then go see the movie in the theater, this is definitely the kind of movie that will look way better on a huge screen than at home. If you are looking for anything other than monster brawls, I would say do not waste your money seeing this in the theater, this is a definite rental for anyone other than Kaiju enthusiasts.
The plot was about as thin as you would expect, the characters all follow clearly(and sometimes painfully overused) action tropes. You have the wash-out, the hard-nosed, the skilled but crippled by self-doubt, and of course the person who won't accept x character into the team because of y reason. It is a paint by numbers action plot that does what it needs to and facilitates the fights. John Boyega gives a mediocre performance, not as bad as Star Wars but nothing amazing. His co-stars do a decent job, none stand out(good or bad).
It is also painfully obvious that this did much better overseas the first time around than it did in the west. There are a lot of painful(and bordering on insulting) Asian pandering moments( specifically China, which makes sense because they have the largest potential market in Asia). I won't spoil anything but they feel tacked-on and jarringly bad at some points, though this will become more and more common as more western movies are allowed into China. They did not ruin the movie for me but they were very transparent and I'm not sure how well they will play in China.
To sum it up, the plot feels paint by numbers, the characters are just good enough to get the job done, the pandering is weird and feel out of place, and the fights were awesome. The CGI was well done and composited very well. If you want to see Kaiju battles on the big screen, see this movie. If you want to see it for any other reason, do not waste your time, rent it instead. Thanks for reading!