I'm finally giving the trilogy another run-through, having not watched them all together in a couple of years...
I must say, I'm a bit disappointed by this installment. G:GotU is a good example of a film that certainly has creative ideas and intentions somewhere in it, but is bogged down by so many technical problems that said concepts are almost entirely too neutered to appreciate. It's not a terrible movie, by any means; but I strongly disagree with the common thought of it, in itself, beating the entirety of Godzilla's Heisei era.
In immediate terms - the film has far too much in it's hands for it's own good, carrying full-on world building, attempts at character-based storytelling, and various form of societal critiques. These aren't impossible thematic tasks; and, when done well, can have very compelling results, as seen in films such as Return of Godzilla or (this very film's spiritual successor) GMK. When done poorly, it leads to none of the wholes amounting to something genuinely entertaining.
The story itself feels very bumpy and indirect (which is in no way aided by the very poor editing throughout). Characters are given almost literally no time to develop, with, surprisingly, too much time being delved to our Kaiju cast. Traces of a distant father-daughter relationship, an environmental message, or an argument on the Government's poor policies are littered about, but are never given time to grow beyond odd one-off scenes that throw off the tone significantly. The cast's time to grow is limited very quickly after Gamera appears, with the story transitioning from watching our characters unveil, to tracing Gamera's footsteps; his existence influencing theirs, instead of the more palpable reversed situation. Without time delved to characters, well-meaning ones such as our female lead come off very strongly as a Mary Sue archetype, with her voice almost always voicing the correct opinions.
Characters such as the daughter or the (oddly) determined scientist have no reason to exist beyond further complicating the plot, both of which could have easily - and logically - been replaced by the nervous policeman and our female lead, respectively. Major plotlines such as why Gamera is connected to the daughter are hardly answered at all; that is, if there is a direct answer, which I'm not entirely sure there is.
Even the visual effects haven't aged well at all. Though Gyaos looked nicer as the movie went on, most puppets and props were very jerky and 'dead'. Gamera had a nice design, but, much like Gyaos, felt consistently fake, especially when flying or simply standing idle. The fights were all dragging and relatively short, as well, never feeling as tense and exciting as they ought to.
Credit where credit is due; there is absolutely a solid film within G:GotU somewhere, but it isn't immediately visible. The monsters, if not underwhelming and lacking of significant storytelling 'weight', are nicely done, and the plot is generally enjoyable, at the very least. And, though they are underdeveloped and as two-dimensional as paper, the cast is absolutely memorable, and work well with the plot.
The monsters are very 'believable', in a sense, and match well with the 'mystic' tone throughout the entire movie; giving both Kaiju a solid, connected origin gives them a fairly more realistic feel.
I can also see how the argument of 'a Showa film done with modern stylizations' could apply here, and thus make some of my arguments irrelevant; however, I feel points such as character and plot issues hold water, as good Showa flicks kept both firmly in grasp.
Despite it's flaws, the film certainly isn't bad - I'd still argue it as a nicely done flick - just very, very rickety. I can't help but wonder if it was rushed in favor of catching GvD's hype.