Hmm... this is actually kind of difficult for me to answer because I bounced really hard off of vanilla Skyrim when I tried to play it. I have a lot of negative things to say about the base game, and the version of the game I like to play is similar but still very different in almost all systems (ie I am a Morrowloot fan)

I guess what draws people to Skyrim is

• Skyrim's visuals are still pretty enough looking (especially the engine update re-releases) that the average graphics snob isn't going to be immediately turned away like they would for Morrowind and Oblivion
• Similarly the combat is approachable and responsive enough to not turn action gameplay snobs away immediately, at least not until the 5000 HP draugr deathlords start spawning
• The explore, combat and loot loop is admittedly pretty well done. Picking up a story side quest and stumbling upon a dungeon to explore on your way there is a satisfying gameplay segment. So is finishing off a chunk of gameplay and hauling your stuff to the market and/or your house
• There is (just barely) enough 'character types' to justify multiple playthroughs dedicated to different gameplay builds (ie evil Dark Brotherhood daedric quest character, College of Winterhold character, Companions werewolf build, Dawnguard vampire run, etc)