Watching numbers get huge without spending hours grinding. It's like the first few levels of an MMORPG every time.
And being able to shift through a variety of styles if I want to, with a really low learning curve. If I want to mix up my playstyle, I can just do it and it's satisfying. If I want to play a completely different type of fighting game character, it almost feels like I have to relearn the entire game.
I'm personally a big fan of active items. DfG, Zhonya's, Gunblade. They're really fun to use for me.
Don't want to turn this into a DotA 2 thread but... >_>
Have you tried it much? I've only very recently used one of my thirty billion invites and tried a few games, and the amount and importance of item actives is just plain overwhelming. Still really satisfying to use them properly, DotA just has a ton more than LoL. Too many tbqh.
As for the topic at hand, I actually really enjoy the super long drawn out games that could go either way. Not talking necesarilly about the turtle and come back games (though those are satisfying too!) but those rare games when no side snowballs and it's just even trades and cautious plays. It's those games where people are actually attentively buying wards and such because they recognize one throw could mean the absolute end of the game if it's their fault. Really brings the competetiveness of the game out.