The Galaxy S8 was the best phone of 2017. The Galaxy S9 is a little better. The Galaxy S9+ is even better. It's up to you whether the size and cost are worth the power: For us, they are.
Feels great in one hand; Excellent low-light camera performance; Better sound and network support than the Galaxy S8
Not a radical upgrade from the Galaxy S8; Larger S9+ model has better cameras, more RAM, and stronger Wi-Fi performance