League of Legends, or LoL for short, is often mentioned as a successful f2p game you should learn from. Fact is that LoL is one of the largest MMO's to date. Of course it makes tons of money for Riot and their owner Tencent.
So why am I hesitent to use LoL as a role model for good f2p models? The reaon is simple: their monetization system is very very specific and only works due to their reach.
Simple explanation: Revenue = Active users * conversion * ARPPU
Their active users is phenomenal high (42 million MAU as of this writing) and this multiplies the revenue formula to the skies.
But their conversion is low, i.e. how many players actively pay. That is my biggest critic. If you use LoL as a role model you might end up with a low conversion and if you fail to get the reach your game fails badly. That's a huge risk. A game can survive with an average reach and a good conversion easily, but rarely the other way around.
Note that the ARPPU is somewhat dependent on the conversion. If your conversion is low your ARPPU can be unusually high and vice versa.
Again: LoL works wonderfully for Riot and Tencent as their reach is so high. Sidenote: their reach is so high due to Tencents reach.