So I did get the Galaxy S2 and it's quite a change from the N1!
The ringer is LOUD
Volume in calls is perfect
The build quality feels very flimsy compared to the metal housing of the N1. the plastic feels too light.
The sound for music, etc is great - not tinny or choppy but good without headphones
The screen is excellent with some beautiful colors
The camera is also excellent, with controllable flash etc.
So if you're thinking of changing, this is a good phone to get, and one that won't have you missing your N1 too much. Especially after you add app after app without even coming close to filling up the available memory.