Alright, so, there are lots of games made daily. This applies to everything on the internet and such. However, some games will get bad reviews and some will get good reviews. Why is that?
To answer that, let's use an example, like Minecraft. No one would disagree that Minecraft is the most popular game. I mean, face it: it has sold more than 100,000,000 copies in one decade. What makes Minecraft so fun is that it is just fun, can keep people entertained for a very long time, has replayability, and it basically has an entire community which grows and expands. It also executes its game idea very well.
So let's just pull out some of these terms here: When I say fun, I mean that it is entertaining and such, and when I say entertaining, I mean that it can keep you busy for a long time. And when I say it has replayability into it, I mean that people will want to play it again and again for hours at a time. When I say that a game executes an idea perfectly, I mean that it executes the game's idea very well and it executes that linear ratio between too difficult and very easy.
A good game would be like Minecraft. A bad game however wouldn't have any of that. It wouldn't be very fun, wouldn't keep you entertained to the point that you stay glued to your seat, no one would want to play the game again after beating it, and it would either be too easy to the point that someone would want to find a new game, or it would be too hard to the point that someone wouldn't want to finish the game or even do it again to get better at it.
Now granted, there may be more factors, like the game would have to have little to no bugs or would have to have some kind of story, but the things I said above apply to any type of game.
I mean, the game always has to have an objective, otherwise no replayability would be in your game. But that doesn't make it a good game nor would it make it a bad game.