150+ hours of game playing, I feel like there's no much left to do other than the Radiant quests, can you people take a look at this? http://img4.imageshack.us/img4/1474/skyrimstats.jpg add to that 265 locations discovered

there's over 500 locations in da game. take to wandering and finding new places and meet new characters to unlock new small quests. buy every house in da game.

have you tried roleplaying as a vampire yet?

Over 500, really? My map is so cluttered by markers it looks like there's no much room left. I've bought almost every house but have yet to buy the one in Windhelm. I'm looking for the gems of Barenziah as an excuse for wandering around [12 gems left]. Roleplaying as a vampire? I'm not very fond of vampires but I might give it a try.

I played over 100+ hours and like you had completed all the main storylines. however, i used fast travel a lot. By cutting out fast travel, on my first walk from Whiterun to Riften i came across about 12 characters that i had never met before and got a whole bunch of new quests, granted, they are the boring 'Collect 20 Ninroots, Find a missing Husband, etc' but atleast you get to meet new characters, hear new dialogue, see new scenery. So just wander and see who you can find. I fell in love when I met Annekke for the first time at Darkwater Crossing. Pity i can't marry her.

what I do when I am bored: I pick a random region on the map that is not explored and just walk in that direction discovering things.
I really recommend going to the hotsprings under windhelm they are very cool and there is a dragonshout on top of a hill there too.

220 hours in, compelted main quest and civil war on mage, completed companions and joined storm cloaks on warrior, completed thieves guild and DB on cat assassin, right now am playing on my gentleman vampire doing RP thieves guild and DB, trying to play as a noble using speech, to become everyones friend, while doing heists and rebuilding guild.

Tons of fun and didn't even collect all dragon masks on any char, nor deadric shrines//quests or clear city quests.... this game has so much gold in it if you know how to mine it.