More slime than Nickelodeon
Saves should automatically migrate to the Steam version if you've already been playing the pre-alpha build, though the developers noted that save files may be made obsolete at some point. Not unexpected for a game still in development, I'd say.
Even though Slime Rancher is considered pre-alpha, there is at least a few hours worth of playtime in the current build, with plenty more to come. I for one am excited.