Been getting into LoL recently, and while I agree it's very polished (I really like the character designs and the free-to-play model is a good one), the one area that Valve could improve on is making it more newbie-friendly. While LoL may be more newbie-friendly than DoTA, that's like saying Venus is less hot than the sun. It's still not a very hospitable place. It's basically a full-time job to get up to speed with all the acronyms, jargon, and conventions. You join your first match of LoL and your teammate says something like: "I'm going jungle Amumu with an AP Sunfire build so I can tank the carry in the lane with my ult when they ping." and then they get mad at you when you have no idea what they're saying. Don't get me wrong, I do like the game, it's just really hard for beginners like me.
Compare the steep learning curve of TFC where you have to master grenade jumping with every class just to compete with how easy it is to pick up TF2. So hopefully Valve will do something similar with DoTA, and make it accessible.