So, I've been playing Skyrim for awhile now without any mods. When I played Oblivion, I used OOO and was wondering if there is anything similar to that out in the mods for Skyrim.

Nope, check back in a year or two

Well, it depends on how extensive you'd like your overhaul to be.

For starters, there's Skyrim Redone (http://skyrim.nexusmods.com/mods/9286) and PISE Improved Skyrim Experience (http://skyrim.nexusmods.com/mods/1269)

For more spawns including a greater variety of different enemies and loot drops (more along the lines of MMM) there's Skyrim Monster Mod and its lore-friendly variant (http://skyrim.nexusmods.com/mods/16411).

There's nothing that does exactly what OOO did (none of these adds quests similar to those included in OOO for example), but by picking and choosing individual mods you can start to get closer to an OOO experience...what was the main attraction of OOO for you?

+1 on the Skyrim Redone and check our ASIS (similar to DLL in Oblivion).