Simply put there is a ridiculous amount of content in the base game. I think the base game these days comes with Morrowind as well so that adds the Warden class. I think, and it's been some time so I could be wrong, that you wouldn't have access to the Thieves Guild or the Dark Brotherhood skill lines without those DLCs. You also wouldn't have access to the Psijic Order skill line as that came with the Summerset DLC.
You'd have access to housing as that was base game, pvp, Warden Class as I said (and Vvardenfell area), max crafting, I believe max level too. You'd be able to respec, and have access to any guilds other than those I mentioned above (or Necro obviously).
Also if you were unaware, Zenimax does occasionally offer free DLC weeks where you get access to the DLC content for free and even keep your rewards and skills you obtain during them.