So far, besides the standard-definition insert footage in King Kong vs. Godzilla, the only really distracting picture anomaly is how visible the splice marks are in the early parts of Mothra vs. Godzilla. They become more sublimated as the movie goes on, and when they have appeared in further movies they're likewise very subtle and not distracting. In the first 15 minutes of Mothra vs. Godzilla, though? They're really distracting.
Currently watching Son of Godzilla. Again, kudos to the new subtitles. I probably watched this movie 20 times, and now everything's just making a little bit more sense.