The current episode of the Casual Stroll to Mordor podcast mentions how Moria is suddenly deserted and more challenging now that players have moved on to Mirkwood. There are many more mobs underfoot now that there aren't players killing them. Ironically, this is somewhat appropriate for the setting. Moria is not SUPPOSED to be a happy fun social place to hang out. It's supposed to be overrun with goblins, not hobbits.
I probably ran through the Mines in the middle ground because I started in on the expansion 9-10 months late. Many players were already at max level, but the place was not entirely deserted, and I was even able to find a partner for a few quests. Even so, I see a major drop-off in how populated the older areas are now that people are in Mirkwood (or instanced skirmishes).
Is this a situation where it is better NOT to have played the expansion when it was actually the most recent chunk of the game, to experience a more realistic atmosphere? Or does the lack of company - and groups for group content - hurt the gameplay experience? It's one of those questions that does not have an easy answer, though I'm just as happy to be spending time finishing Moria before I brave the Mirkwood masses.