I found LOL much easier to get into than DOTA, but that is personal preference.
As for the world championship, well this game has become massive with 9 times more viewers this years championship than last years. Estimated that there are over 8 million players, and the viewership on Twitch.tv for LoL is rarely under 100,000 during any time of the day.
I love the game, its a simple 5 v 5 game where you pick a champion to control, the basics are Attack damage Carry which typically run bottom lane with a support class (think healer). Mid lane is your Ability power carry, think mages. Top lane is your bruiser or tank, but there is a lot of playing around with all these roles depending on your rank.
Jungle is the one I'd recommend newbies avoid, this is the one role which you should have a good sense of the game before you start to try to master it. The best starting roles are either support bot, mid lane, or top.
The best advice is to just start playing, to get a leg up on other new players use the guides here:
http://www.lolking.net/guides/
It will give you tips on what to level up, what items to buy, and of course watch twitch.tv streams, the best streamers to learn from are:
http://www.twitch.tv/nightblue3 - Mains jungle but does take other roles, you can learn tons, great stream.
http://www.twitch.tv/wingsofdeath - Famous top laner, but has been playing a lot of other roles lately, another excellent streamer who explains everything.
http://www.twitch.tv/tsm_theoddone - Calgary boy who jungles for the most famous LoL league team, Team Solo Mid, he's a jungle main, very funny and enjoyable guy to watch, you learn a lot watching Junglers.