Don't get me wrong; the core gameplay itself (imo) is vastly improved and improves upon the DotA model. The summoner-specific customisation/levelling, runes etc. is a great way of adding complexity and variation in hero builds without the need for new shiny items etc. Getting rid of denying altogether, while a somewhat controversial choice, simplified things and shifted focus solely upon last-hitting which eased the burden esp. on new players. And all these things are the reason why I want to love the game like I did in the past.
Crystal Scar was added a couple years after the game's inception. It was a fun and fresh way to spice up the game but apart from that it's been nothing but new heroes.
I just don't want a MOBA game that insists on adding more and more complexity each time they make an update. I want Riot to focus on making *all* their current characters more viable and less obsolete, because there is still a certain percentage of characters which, while are great fun to stomp pub matches, are rarely used in competitive play because there are simply other heroes that do a much better job of it.
Riot may have changed their tactics recently, I don't know. I haven't played the game in the past few months because while I was always willing to learn the finer points of LoL, having to constantly learn how to play/play against a new hero was tiring and I was finding it difficult to keep up.
It's a popular approach to adding content to the MOBA, and for plenty more hardcore players they have no trouble with that. But by principle alone it's not for me - like I said in my analogy, it's like adding a new character each month for a competitive fighting game. The metagame is already so complex, you don't need to keep messing with it.