Maybe you could call a game "complete", when all the emergent properties arising from the mechanics of the game, have been explored in detail.
Wouldn't this definition indirectly imply the following?
If a game that was generally thought to be complete gets an expansion, sequel or mod that only adds new content (but does not change the mechanic) than this would "un-complete" the original game. But I get your point (and I'm possibly just Semantics trolling by stating my objection to that definition). The goal of game design perfection is to completely explore the possibility space of the mechanics.
But perhaps "complete" is not the even the world I should be using. What I mean is as state of completion where the game can be described like this:
"Ur.. Umm.. You can like play it from the beginning to the end and yeah maybe you could consider it complete even though there is possibly (or even obviously) more room for improvement. It's like a full game. At least nothing obvious is missing."Perhaps the word "completable" is more like what I'm searching for than "complete". A game that should possibly not be released to the general public yet. The existing content has the indented final production quality. It id definitely ready to be released – not only as play testing or as a demo – but as a shorter version of the final game. Not single vertical slice, but multiple vertical slices stacked together in a manner that is indistinguishable from a finnished game.
(Edit: Proper grammar! Just a little bit..)