Don't even care if it's been quoted already, this thing is beyond ridiculous!
For those that are running Act 3 and Act 4, care to share your routes? Act 1 and 2 routes have been shared a few times, but I haven't seen too many for 3 and 4.
If you have a lot of time for Act 4, just start at the 2nd quest, WP to Vestibule of Light and fight one or two elites, then Rakanoth, and continue on from there until Izual and Diablo. Act 4 is pretty short and there really aren't many routes to go. If you're shorter on time you can do what that wizard and I have been duoing lately. We usually start the game at the 2nd to last quest, waypoint to Garden level 2 and fight from there until you get to Izzy and then outside Diablo's door. Now you'll want buffer time for big D himself, since he can sometimes surprise you. So what we do then is WP to Vestibule and continue until we find that first elite group (usually right past that in Garden level 1 or if you have bad luck it's just a bit further into the level). Then we TP back, repair, and hit Diablo with almost all our time left on the NV.
Keep in mind if you do the "shorter" route you're putting yourself right near the end where the elites are a helluva lot tougher. Those Morlu Incinerators are probably the worst enemies in the game hands down. They teleport, slam a meteor on your head and then teleport again before you can get more than 3 hits on 'em. Sometimes you will have to skip them. Also, because of things like those you have to do things cautiously in this area. Skim along the edges and pick off only what comes to you. If you dive head-first into the center of these areas you will die a lot and you risk ruining your run by basically blocking off whole levels. So, go around the edges and kind of double back to create larger paths to lead them down. Make good use of the bridges and pull elites back to those. Sometimes your DPS can sit on the other side of a 2-sided bridge while your tanks can be on the other.
Otherwise starting at the 2nd quest and going on from there until you hit a wall is pretty decent. The garden levels, while not abundant in Elites like some of Act 3 are usually not too hard. The level itself makes it really easy to kite and gives you nice natural circles should you need to move them around and reposition a lot. And, generally speaking, you don't get huge insane groups aggro'd with your elites like the later levels.
Also, just skip the purple bosses altogether and punch any teammate who accidentally clicks one and aggros it during another elite. They don't drop much of anything and they're a waste of time.
Don't have good enough gear to farm act 3. Do 3 act 2 runs don't get anything I can even sell, much less an upgrade. Go to the auction house, no upgrades for less than 10m/$30.
Kind of makes me not want to play.
There's no way this is true. If your upgrades are costing that much and you still can't get through Act 3 then you're doing something wrong. Granted, if you're expecting to farm Act 3 and 4 like you can 1 and 2 you're crazy and yeah that takes a lot. Act 3 and 4 take time, but the drops rates are better to compensate. But, really, if your upgrades are costing 10m per piece you should be able to get through Act 3 well enough. I've got things I could probably upgrade for 5 or 6 million that I don't really want to spend that money on, since I'm financing my DH through Act 3 now too (that and I don't actually have 5 or 6 million), and I can farm Act 4.