how to determine if the game is more or less enjoyable ?

Simple don't go look the number of players => this is a biased statistic because they will raise with lol's fame and esports. Plus having new players that play once per week it isn't really a plus value...

Look at the number of hours played per player per day and this will tell you if people enjoy it more or not.

Even if the numbers of players raise it won't really say that lol is in a good state or not. The game won't die but if there will be less games played per player that means a lot.

I hope that we will have access to this data one day...