Not enough sidequests:kg2
there are plenty of side quests and activities you can do. Ive gotten so many quests just by opening a book.
I would recommend both DLC's but thats cuz i think the game is awesome. youd have to talk to the Skyrim expert LadyCroft
to find out if Dawnguard and Hearthfire are great add ons.
for most fun i would suggest you focus on magic types like enchanting, conjuration and illusion. i tried Destruction my first playthrough and even became a master at it but didnt like it. My next when i focused on Illusion and Alteration was the most fun. Just being able to calm or pacify a group of hostile bandits was fun, hell ive calmed giants and Frost Trolls and even made them run away in fear. Conjuration is fun for the summoning and with that you can try archery since you can summon an awesome bow.
I could go on for a while lol. LC told me how much fun enchanting and alchemy was and when i tried it i loved it but that was with a new character, she told me block so now im trying it out. Just focus on 2 or 3 things per character cuz you really cant become a master in everything really. you can get all 100s but really doesnt mean ur a master. My first character was a 100 in conjuration but i could do no spells at all.