Once you get to level 50, the expansions will certainly be enough to carry on playing. You'll easily get to 60 in Moria. Mirkwood will easily get you to 65. Isengard is much more than enough for 75, and the Rohan expansion is comfortably enough to get you to 85. You'll visit the other zones as part of the Epic quest series, but you don't need their content in order to level up.
Originally Posted by Mavver
Before level 50, I recommend Evendim. After that, either Angmar or Forochel and maybe Eregion, depending on what you want spend.
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