Lv30-40 is easily the dullest part of the storyline. You get sent on a long chain of quests where the NPCs even make it clear to you they're just wasting your time and have little to do with the actual story.

After that, things get much more interesting, especially as you approach 50. If you need an indicator, I'd suggest you start paying more attention to the story once you beat the Titan story fight.