What to do when you feel 'done'?

So, I was working on a project, this one to be accurate . Got it to a point when I feel that I put in the content I wanted to put in.
However, there is more stuff I can add to it, like a mission system, but I just have the motivation to do so.

Has anyone been in that situation? What do you do to keep going or do you just put it on hold for a while?

BTW, it’s not a major project, it’s just a concept.