This video shows the Achievements and Profile UI in action. Some of these were introduced in the latest Diablo III Beta Patch 6. The video also shows how to create a Coop Game, and how to join an existing Coop Game.
What I am seeing in beta so far is that Coop players run through the dungeons without breaking vases, checking bookshelves, nor fighting mobs much, except for rare mobs. They run around searching for the doorway to the next Cathedral level, and then rush the Skeleton King.
Hopefully, this doesn't become the norm, but with a game as long as Diablo III with about four Acts, this is bound to happen. While live streaming, I noticed a lot of framerate issue in intense fights with Physix and Shadows disabled. Seems the EVGA GeForce GTX 285 will need replacement before Diablo III goes live. Check out the video. Note: Click the full screen button located at the bottom-right corner of the video player.
After a few days, I have completed all the Diablo III Beta Achievements except for one that requires players to resurrect each class in Coop mode. I have been close to dying, but so far I have played all five classes without a single death. I didn't feel like asking others to relinquish their no-death streak.
You can max out your character to level 13 in about one and a half runs through the Skeleton King Act. Took me about three days to Max out all classes to level 13, with pauses in between of course.
Completed Achievements Gallery