"Must have apps for this phone" is dependent on the user. However searching this forum, one can find a few threads covering this topic already. There is also the "F.A.Q." (Frequently Asked Questions) thread at the top of the forum.
I would also suggest looking at www.youtube.com and watching N2 videos. They have a lot of feature and app videos that are pretty informative.
I think it would probably help if you tell us exactly what you would like to do, in order to give you proper suggestions and clues as to what the phone can do. Not everyone will have the same take on "what's good" about the Galaxy Note 2...and more generally, for Android. Let us know what are the most important things to you, as well as things that you might want to do, but are not sure if it's even possible.
