sure this game is not boring(for me of course),but sometime i need to get a pause from tb,or i start to hate it.But after some years i guess i wouldn't be a human if wasn't so..
I think this game can give enough reasons for continue to play it year after year: you start as a noob and the desire to become good can keep you busy for at least 1 year.Then you see the possibility to become REALLY good,so you can go on 1/1,5 years more,in the while you start to know people and maybe join/made a clan.If you did these 2 last things well,so after you became really good you can still have fun playing with these persons.You don't care anymore SO much to become better(even if you never stop to learn this game)ingame,but mostly to play with the awesome people you have know in the past years.
This is how it worked for me,but i'm sure that,for example a dueller,had/has different stimuli respect me