On a wing and a prayer...
Mothra and Godzilla have similarities in their respective film history, namely their original director, large monsters and the atomic bomb. Mothra comes with its glittery fantasy elements and Godzilla more of an aggressive tone and perspective. At least, they started this way. Combine to this a subplot somewhat forcing humans to interfere with the main story and you get a weird little mix.
Although sometimes played for a laugh, the performances are highly animated to match the signature ridiculousness of the creatures. We know we're getting further from our original material; two hybrids of science-fiction, fantasy and horror with a commentary, and turning a collection of invasion films into a wrestling match. This is, again, a fully-lit visual treat with an inviting aesthetic.
It's hard to look past the cheese when that's all there is. Those miniature singing twins, the Cosmos, as they call themselves, can get annoying but that song sure sticks with you. Fortunately, there are major improvements on the effects in regards to the evolution of both franchises, Godzilla and Mothra, that is, but, in the end, it's too bad we get so much preliminary and so little monster time.