My roommate just got me into this. It's good fun, but very complicated for a newb. I haven't run into these rampant trolls yet, but I also haven't actually played a true PvP game yet, either - all Bot matches.
The biggest thing that sticks out to me from browsing the LoL forums and subreddit is that the community is constantly engaged in bitchfits about various champs being OP or weak, etc., etc.
What I've found is that there is always a counter to another champ if you build the right build or play to counter that champ. The efficacy of most champs is entirely subjective based on the people playing - their skill, map awareness, knowledge of items and champs, ability to pull off more complex zoning/jungling/ganking. For every group bitching about Trondomore!!1+shift, there is another group listing counters to him and ways to outplay him. As far as I can see, this is the same for every champion. IMO, entirely subjective.
ETA: I'm Tarcanai in-game, btw