Until this movie came along, in my opinion the original Godzilla ('54) had the highest production value in terms of reality of the monster. Gamera 1999 sets a new standard in kajyu movies with the new level of believability it brought to the monster's character. The fight scene in Shibuya is absolutely believable, and integration between CG and live humans are tight. Cinematography is beautiful, and there's no artificial quality to the scenery.
If I had complaints about this movie was that special effects director Shinji Higuchi seems to like to design monsters that are metallic looking and doesn't have a mouth (Legion, Iris). I think mouth is one thing that express monster's feelings and there was total lack of communication about the aggression Iris had towards Gamera. Legion at least had eyes, but Iris only has one light bulb inside the head. It looks a bit like a robot which took away from the involvement two monsters had for each other.
They brought back Nagamine (Shinobu Nakayama) to the story which was the right move, but neither she or Asagi Kusanagi (Ayako Fujitani) was at the center of the story. The girl Ayana wasn't strong enough actress to carry the lead and once again, story lacked a focal point as it did with Gamera Attack of Legion.
The '90s Gamera series gets darker and darker as the series progresses and this one is the darkest of them all with Gamera being total engine of destruction. It made the movie authentic but at the same time took something away from the Gamera character. It had no involvement with the human beings. I wish they would make Gamera 4 with plot line returning to like that of the first '90s Gamera movie with strong casting of characters.