To be honest the "special shadow mario acapella music" levels in Sunshine were kinda annoying after a while
Everything else was cool but i somehow like Galaxy so much better. It feels like the good old 64 but with awesome ideas and leveldesign.

I just finished the story yesterday, and now i'm going to collect all stars. After that it's time to get the second galaxy game

I'd not recommend that. Those games are very similar (more so than usual for Mario games). I'd assume that you'd get tired of it way too fast if you were to play the second game right after the first.

Instead, get Another Code: R

or red steel 2.

or Resi

Onechanbara.