This is an almost flawless game with server difficulties.
After playing the game for a solid six months I would give this game a 8.5 out of 10. Now when a person starts playing the game, if they have never experienced an AoS style game before they will be lost and confused. Most likely the player will lose the first couple of matches until they memorize how each ability works. The learning curve is steep, but once the basics have been mastered does the game truly start.
The greatest strength of League of Legends is the strategy behind it. There are almost limitless combos which players can pull off with both their heroes and their teammates. One example of this would be for a person to disable an opponent, this would allow his teammate to easily hit the disabled opponent with a skill shot(an ability which hits the first unit). On top of the strategy for the skill combinations, there is also the many different item builds. Almost every champion in the game is able to play 2+ more roles. the game encourages players to try out new builds and try to discover the best combination. One champion is called Shaco, he is an assassin type character with many builds. The main ones played are AP shaco, which turn him into a ranged hero; Crit damage shaco, which turn him into a melee burst damage type hero; Sunfire Shaco, Gives him extremely high survivability + AoE damage; and finally DPS shaco, which gives him sustained DPS. Each of these different builds give him a different play style to an already complex champion. Even after all this, Riot has added rune pages(small boost to heroes), and Masteries(Think talent points for every hero) for further customization and strategy.
The greatest flaw of League of Legends is the downtime of the servers. While the game itself has very few flaws in it, The servers are usually preventing you from joining. Additionally due to the game's popularity this problem has just increased in size. A second problem with the servers is that riot is constantly having technical difficulty, in fact one day the servers were down for nine hours while they tried to fix the problem.
In short League of Legends is a great game to play, but be prepared to lose the first few matches. Also be ready for some downtime if the servers become busy or there is a technical difficulty.