Pros: F2P, Multiplayer, fun, strategic
Cons: player community is very negative
I started league about 3 years ago. At first, I hated it. but that was because I was playing alone. This game is based on mutliplayer experience and working as a team, you cannot win the game unless you work with your team. If you like to do your own thing, then this game is not for you and you should probably go play a game like Halo. LOL is a very fun and competitive game, plenty of players stream their games on twitch so you can always learn from them and their mistakes.
One of the best things about league of legends, is that it is not pay to win. anything bought, that gives an in game advantage can easily be unlocked by just playing. So this game does not follow the typical pay to win playstyle.
The worst thing about LOL has to be the player community, being a competitive game, drives the appearance of trolls and players who are just mean. But in all honesty, this happens in just about every PVP driven game, but in LOL it tends to be worse.
I normally only play league when I am in-between games, but recently it has been my "main" game for a few months, being free to play makes it very appealing and having friends play it makes me keep coming back.