QuestHelper is kind of like Routes for quests. There's no other UI for it. Just the routes on the main map. It uses animated dotted lines moving in the direction you're supposed to be going on each one to help you out with where to go next or if you want to skip around, which way you should be heading from a certain area.
It has icons for killing, collecting or quest npcs to talk to. When you mouse over icons for kill targets, it'll show you heatmaps for the areas that mob has been seen in and a tooltip that says what quest it's for, what mob and how many items you need to collect, if applicable.
There's no other UI for it, which really does fit in with what some of you are suggesting about minimalistic interfaces and addons that just provide a feature and stay out of your way otherwise.
I agree that this thread hasn't really been too much about "the next big thing", but this particular addon (that I only found recently) was definitely a "wow, how did I live without that" addon. I used LightHeaded before, but it's just a lot of information you can get directly from wowhead and the arrow? >.> *sigh* It gets in your way. IMHO, I'd rather have a minimap arrow, but even an icon on the main map is good enough.