Although not a popular choice, Gamera 2: Advent of Legion is my favorite of Shusuke Kaneko's films. It feels different from his other work, going more for pure entertainment without much culture dissection or deeper and more extravagant plots involving mythology. It's a simplistic but well done story of monsters vs aliens, to dumb it down to its core, but that undersells the success the movie achieves from its approach. The story pacing is excellent, with the right mix of action and mild humor to carry the film despite some weak characterization, while the special effects and musical score help the production to shine compared to the wealth of alternatives in the genre.
For the story, the movie opens with a meteor shower slowing its descent toward earth. The objects turn out to be an organic life that quickly takes root in a nearby city, causing vegetation to grow as casualties mount. The Sapporo Science Center, through Midori Honami and Obitsu, begin working with the military to try and determine first the unexplained instances and then later the creatures themselves. They project that the vegetation is actually preparing to seed, creating a nuclear-level explosion in order to send the seeds into space and populate another planet. Before this can happen, Gamera arrives, destroying the vegetation but causing creatures called Symbiotic Legion to attack. After the Legion are fended off, the creatures move to the heart of Sapporo, flanked by their gigantic queen. Gamera arrives to stop them again, narrowly succeeding, as the creatures move toward Tokyo for a final offensive while Gamera is incapacitated.
The movie undoubtedly feels different from the first and third entries in the series. The approach is almost more American, circa the 1980's, in the outlook on characterization, casualties and slight mix of humor that is a little bit more refrained from the previous Gamera movie. If anything, it dumb's down the subject matter compared to Kaneko's other films, but as far as popcorn entertainment goes Gamera 2: Advent of Legion excels. The action pieces are great, the concept of aliens invading is given an interesting direction through the seeding motivation, and the movie is self-contained and satisfying while making just enough references to the first film to pay off for genre fans. The stakes feel high, and Gamera really asserts himself as the selfless hero in this film who is against the odds, standing out distinctly in characterization from Godzilla. He feels a little out of place in the production, as ultimately the focus is on Legion and her story while Gamera arrives on cue to save humanity, but in a way it only makes Gamera's heroics shine, as the creature's only vested interest is to protect the Earth from a new threat.
In terms of acting and characters, Toshiyuki Nagashima does a fine if not memorable performance as the stern colonel lead. He plays the role mostly straight, which works to develop some minor chemistry as both Miki Mizuno (Midori Honami) and Mitsuru Fukikoshi (Obitsu) give performances which can often drift from serious to subtly tongue-in-cheek. There characters aren't particularly deep in regards to characterization, but there is enough meat there to at least carry the movie from start to finish thanks to great pacing. The female lead, Midori, is a mix between the damsel in distress at times and the director's penchant for stronger female leads. Suffice to say, she doesn't measure up to the leads in the other films in the series, but adds a bit of a humor to make her likable. The reoccurring characters are down played a bit here, making it still feel like a sequel but also the odd man out since the story doesn't deal with the Gyaos or heavily with those that were established in the 1995 film.
For the special effects, Shinji Higuchi is once again at top form. He's improved even more from the his work on the first Heisei Gamera film and is at that stage where his passion for the genre and his craft shines. For a kaiju production, the SFX are remarkably consistent. There are a few bad CGI shots, in particular with Gamera's battle with the Symbiotic Legion, but the suits themselves are fantastic and effects like Legion's beam are amazing to behold. Legion in particular is extraordinary in execution, with a gigantic suit that actually creates the very real illusion that it's not suitmation.
As for the music, Kow Otani gives a decent soundtrack, although it doesn't measure up to the two scores that bookend it. His Gamera: Guardian of the Universe (1995) soundtrack was remarkable, introducing a lot of fantastic themes with great variety. Otani's Gamera 3: Revenge of Iris (1999) score took a more somber, mysterious and unearthly route through more synth work that felt unique. The soundtrack for this score sits in between those, having an adrenaline pumping theme for Gamera and Legion's first bout but not having nearly the number of memorable themes that the other two productions do.
Overall, the movie feels like a more traditional "summer blockbuster" and in that approach succeeds. It's nothing profound, and in some ways that's welcome as one could argue the follow up film, Gamera 3: Revenge of Iris (1999), tried too hard to seem deeper than the subject matter was. Those looking for a solid film, catering well to what the genre is best at, have a safe choice from the second go with the Guardian of the Universe.