What people seem to fail to understand is that there's a massive difference between aesthetically appealing graphics and technologically advanced graphics. Super Mario Brothers 3 is technologically awful, by modern standards. So is Chrono Trigger. But games like this have good graphics, as in they are nice to look at despite the technology. I'm sure you can generate your own list of top-of-the-line graphical games that are, in fact, really ugly and just not visually engaging for whatever reason.

Good graphics are very important; advanced/groundbreaking graphics are not at all.

As for the general question, there is no defining feature which makes games worth playing. It's always a combination of those things.