If it is a short game like 1-3 mins, then it is better to be interactive or fast paced or pleasing to look at.
If a little bigger like 10-15mins, then I'd say it should be replayable or interesting so people actually play the whole game. Like maybe have a small goal to reach and show it with a progress bar to motivate people to complete it. Just my opinion tho :)
Depends entirely on what your game will be, some types of games need to be longer than others, like you most likely can't make a compelling story within a game that is 3 minutes long. Short games are very common in jams though, so i think you shouldn't worry about the length and rather the polish of the game.
