The bulk of my time with the 3DS consisted of playing the Pokemon games, Ocarina 3D, FE Awakening, and Animal Crossing New Leaf.
I fell out of Pokemon not long after Sun and Moon, but I was getting frustrated with the series even earlier than that, around the time of X and Y. But SM and USUM were the straw that broke the camel's back - the constant unskippable cutscenes killed the pacing of the game for me. Rotom phone didn't help, either. The games felt overall more sluggish when compared to Gen 5, and the Pokemon themselves seemed to lose some of their charm in the shift to 3D.
I loved FE Awakening. I have a soft spot for plots that put a major focus on the concepts of time, and I liked the pair-up system, as it naturally made it easier to increase support levels. Character sprites on the maps look very well done, critical attacks have really fun trigger animations with the cut-in headshots of characters, and the combination of skills being affected by inheritance all together made for a great time. There are still some issues I have with the game in its difficulty and story to a degree, but I loved the game regardless.
All in all, while the system didn't have as strong a library as the DS before it, the 3DS still offered a true handheld game experience, which almost feels like a lost art nowadays.