Mods
It is highly likely that you will never play Skyrim in a vanilla state again after playing with mods. The reason being that Skyrim had problems, and everyone had different opinions to what those problems were. Say, for arguments sake, you think the swords are too short and wide. There’s a mod for that.
Skyrim has been given an immeasurable amount of content through mods and the modding community. Yes, some of that content is of questionable quality and a lot of it just turns Skyrim into interactive pornography, which is no where near as fun as it sounds. The silver lining is that there are some absolutely amazing mods out there and they have all been time tested by the community. So unless you go looking for it, you shouldn’t find too much weird stuff, but this is the internet.
It is also easy to install the mods. The most popular site for Skyrim mods has its own installer/downloader, so all you do is click a button to download the mod and another to install it. Providing you are not running six gazillion mods at once, you should be fine, but you probably will experience compatibility errors.
This is by far the most common reason for replaying Skyrim. New mods come out daily so it’s really just a matter of time before one comes out that interests you. You’ll find yourself frequently saying, “Wow, wouldn’t that be a good mod to have from the start.” And in seconds you’re hooked, it is just phenomenal.