I have been using this about 1 week and I like it much better than Aperture 2. A2 was always a bit cumbersome. A3 is almost as easy to use as iPhoto and has a lot more features. I doubt I will ever use most of them though (I never used "faces" and other stuff in iPhoto).
I was also pleasantly surprised to see A3 seamlessly works with my Nik Software plug-ins I had used on A2. I use the hell out of Nik Software Silver and Color EFX and no problems with A3.
Overall, I think I am pleased. I am still on my free trial of A3 but think I will make the switch. I used to use iPhoto then import select photos into A2 for advanced editing. I was hoping I could use A3 for everything and I think it is very doable.