Yup. Of the various game genres, it's got one of the steepest learning curves. Learning 90 champs and their 4 abilities (plus passive abilities) is a slow process. Mastering them is another level. Just read my first post and the tips for new players. Following those will get you started in the right direction.
And ignore the trash talkers. You get a lot of people who think they're the best players and that it's bad teammates that are holding them back.
What he said. Even then, learning multiple roles for various champs and mastering those roles can get more complex.
The two simplest roles to master are bruiser and passive support roles in my opinion. Bruisers are champs that can get into the mix of a fight, take a few licks and dish out a few licks in return usually. Passive support champs hang in the back and keep their team going as best they can with healing and buffs.
Out of all the champs to start playing and learning, here are what I consider the easiest champs to play and do well with. These fit into just about any team composition and don't require as much strategy to win with.
Sona (passive support)
Garen (bruiser/tank)
Singed (bruiser/tank)
Caitlyn (ranged physical damage)
Cho'Gath (bruiser/tank)
Lux (ranged magic damage)
Those champs can fit anywhere in any team comp. They may not all be the "best" at a given role, but they will all do well. They are also all ridiculously easy to play compared to other champs that are similar in nature.
If you are looking to purchase a champ or two I highly recommend getting one of the ones I list above if you are starting out now.
The game is a strategy team game. As such to do exceptionally well requires time and effort into mastering various champions and roles. It also requires at least learning what all the champions are capable of even if you can't master them.
Eventually through playing you'll learn your strengths and weaknesses for various champions and roles. I myself think I make an excellent jungler, support, tank, and bruiser. I do alright as ranged AP (magic damage), and can play ranged AD (physical damage) decently. I'm not the best at the ranged based champs at all. Just not my play style as much. Even with support champs I only play Sona and Alistar with great skill. Taric and Soraka are support champs I don't do as well with for example. I just haven't taken the time to master them although I have played with them. I found they, Soraka and Taric, didn't suit what I like to do in the game.
The game can be taken as laid back or as hardcore as you want. It can be fun either way. As others said don't let the kids and the raging emo players get you down if you find the game fun. Remember this is a competitive game and people like to play to win. Many people get so pissed off the moment they start losing though just like any other form of competition such as sports. You can either laugh at them or ignore them is what I recommend.