It's a nice little game. Its structure is pretty unique as far as brawlers with RPG elements go.
Its as long as you want. You either play by the rpg system's rules or you get good and go straight for the bosses regardless of level except a high amount of Willpower.
It's nice in a sense that it wastes no time and you're constantly progressing (aside from the times you have to grind.)
Difficulty curve is pretty balanced as well.
Combat is pretty tight similar to its NES sister series, Double Dragon, as well.

Overall, very good beat em up and pretty great NES game.