I reinstalled the game a few weeks ago after not playing for ages due to a constant feeling of never finding decent items and being tied to the AH for upgrades. The game (even just post patch, not even counting the xpac) is so much more playable. If you're on the fence, I can give you a few bullet points that have kept me interested:
1) With the AH gone, way more legendaries and meaningful items drop.
2) The drops (both rare and legendary) are often more meaningful as they cater the stats to your class for the most part.
3) All items (including legendaries) roll max-level with appropriate stats for the person who made the game.
4) +Skill and +DmgType has become very prevelent stats on many pieces now, making it less about sheet DPS and cookie cutter builds and more about building a spec that compliments your playstyle and the gear you've found.
5) Paragon levels are shared across all characters so no more grinding paragon for all your toons.
6) Paragon points are used to supplement stats like Int/Dex/Str, Vitality, Life on Hit, Crit Dmg, etc, allowing you to customize your build further and fill in the blanks your gear lacks.
All in all, I really like the changes and what little I've seen that they added to the Xpax (namely the Mystic for customizing drops in both appearance and stats) I like as well.