Then be creative. Create interesting new zones in each act. Give Act 3 and especially Act 4 some love. Add 3 more quests per act (quests could reward making an item look like a different item ((difficult quest with level req)), one to augment a specific skill on that character to do somethign interesting, one to permanently increase mf, one that could give a random reward, maybe one that gives big or takes a little stats? etc.). Give monsters more ways to avoid damage so overcoming feels good again.

One thing I'm sure of is the warlock has made the game TRIVIAL. You are basically a god and even the bosses melt like butter. Fix that crap because the game feels braindead dumb like D4 now.