Screen Play's Jason Hill reveals the interesting premise and features in MySims. For examples:
MySims has a story. The story premise is the player has to revitalize a town that has fallen on hard times, and it's up to the player to rebuild the town and attract different Sim characters (there are 80) to move into the town.
The player needs to collect "essences" from different tasks. Different essences are required to build different items to appeal to different Sims like the musician and scientist.
Different areas like the desert and forest have different goodies and Easter Eggs to be found and collected.
The Wii and DS versions are completely separate products and do not interact. The DS version is set on an island and more goal or mission orientated than the Wii version.
The article reveals these and other features in more details.