It's a significant improvement upon the first game. Update art, improved mechanics, better online multiplayer support and some new content. If you loved the first, you'll love RORR.
What were you expecting? This is for those that found RoR2 3D to be underwhelming (in that, for me it's really overwhelming to play). RoRR brought all the features I liked in concept and applied it to the format I loved: pixel art 2D.