Each other creature copies the printed values of the targeted creature, except that they aren't legendary. They won't copy other effects that have changed the targeted creature's power, toughness, types, color, or so on. They also won't copy counters on the targeted creature (they'll each just retain the counters they already have).

If the targeted creature is itself copying a creature, each other creature will become whatever it's copying, as modified by that copy effect.

This effect can cause each other creature to stop being a creature. For example, if you target an animated Vehicle, only the printed wording will be copied—the crew effect that is making it a creature until end of turn won't be copied. Each other creature will become an unanimated copy of that Vehicle.

Non-copy effects that have already applied to the other creatures will continue to apply to them. For example, if Giant Growth had given one of them +3/+3 earlier in the turn, then Nanogene Conversion made it a copy of Bear Cub, it will be a 5/5 Bear Cub.

If the targeted creature is a token, each other creature copies the original characteristics of that token as stated by the effect that created the token. Those creatures don't become tokens.

As the turn ends, the other creatures revert to what they were before. If two Nanogene Conversions are cast on the same turn, they'll both wear off at the same time.