Yes, for me wow is still immersive.
but then again i spend a lot of time playing by myself, rarely doing BG's / Dungeons
i think the best moment in pandaria was when we opened the gates to the vale or defended Stoneplow.
another series of strong moments for me personaly was the Li Li & Chen quests, trying to track down the other Stormstouts.
it all depends on your prespective if you ask me. Vanilla wasnt "more" immersive, it was just new... thats just my 2 cents anyway.