Mabinogi ^^but you need to pay for story (its f2p game )
f2p games havent good storys .They focus gameplay (mostly its the first factor)

When i think about f2p storys ..hm cabals one? RoM (have more then one) ?
Domo? (dome have a good one with cutscenes)
9 Dragons have a nice Story about the History in the old china ( very good texts)

and so on