The game is extremely polished. It feels like the old NES games we remember from our childhood. However, it has many modern game mechanics that make it a better game, and it is a keenly crafted and designed games.
The graphics and animation are beautiful and although it 8 bit, the art style doesn't feel 8 bit or ugly. Instead it is charming and the detail and personality provided in the animation is inspired.
Not having a certain number of lives and having save states make this game much friendlier to players. Everyone should be able to beat this game.
Platforming is carefully designed, and although it maintains many elements of old school games, it tweaks the experience to make it more playable and forgiving.
In the end, this game deserves all the praise it has received and it is not just a Mega Man clone, but a tribute to an entire generation of gaming.