A game with open source is better than the same game with closed source, basically by definition.

A problem open source games tend to have, is that they often have an overly democratic development process. Art by committee can at best closely resemble another piece of art. It also makes it hard to reject ideas and kick out people who pull in the wrong direction.

The focus also often ends up on the code being presentable rather than the game being engaging. Real games that are made in reasobable time and have the necessary tons of little tweaks and adjustments needed to be fun have HORRENDOUS code as a result. Few developers are willing to settle for that if they know the world will scrutinize their code and judge them for it.