I believe most (if not all) don't have any issues...

Good however, is very subjective, while people liked/used that Twitter widget is kinda useless for me since I rarely use Twitter...

Gaming wise I believe atleast Angry Birds and Bounce and mandatory to have fun/see the 3D part of the N900.

Others might be useful like the Speedometer or whatever, just browse some and see what fits your usage of the device.