Can't really say, with PSN down, i didn't get a chance to try the demo out.
I don't see there to be a demo, I only saw the trailers.
I remember playing the original game like this:
1. Lead the characters to a horde of monsters
2. Walk away, prepare a sandwich/get a drink
3. Come back, monsters dead
4. Press health/man/"collect loot" hotkeys
5. Repeat steps 1-4
The second game was more involved but some annoying bug kept me from enjoying it when the expansion was released.
I'm hoping the 3rd game has a more interesting story
yeah the first game was generally like that, if you do things right you just do that, horde, take a piss, back horde dead, bosses were tougher in the second game, nonetheless it was also fun, I didn't play the expansion, it wasn't needed anyway, it should have been part of the original campaign.
The demo kinda hooked me so I will likely buy the game in a few months, I already know there are a few annoying errors in the release game so I will wait for a patch.