To be honest Undertale is the only one I can recall off the top of my head that left a lasting impression. Witcher 3 was good but I had some problems with how it structured the character building aspects and I wanted to just get back into it once the other expansion comes out. From there I'd just struggle to think of ten games from 2015 that I played from this year. Which doesn't feel fair for a list.
Also, Splatoon?