What are the pros/cons/differences between Disgaea as compared to Disgaea 2 & 3?

I thought this would be a fun topic to start off the chatter on the Disgaea Game Series niche' board.

What are the pros/cons/differences between Disgaea as compared to Disgaea 2 & 3?

Feel free to discuss in as much detail as possible to help those still fairly new to the game series,
(Try to leave out game spoilers.)

I would analyze the three myself for you but i've only played the 1st Disgaea in-depth, the 3rd Disgaea for very little, and I haven't even got to try the 2nd Disgaea yet as i'm still working my way through the 1st!