What is there to do on Runescape?

If you're only level 53 then you have not finished all the quests. You've maybe finished all the f2p quests but there is a lot more to the game in the members world. If you can afford $5 a month then try it out. If you can't or if you simply would rather spend the money on something else, that's fine. Just move on to a different game if this one is boring to you.