The Therapist Gamer

Strider is a "Metroid-vania" style game where you technically can go anywhere on the map from the start, but you will gain abilities throughout the game that allow you to uncover secrets or reach additional areas. Your basic form of offense is a sword, and you earn 3 additional blades throughout the game. You can also climb walls and hang onto the ceiling with minimal effort.

I got this game for free, but I think it's normally $15 or so. The game can be completed in just a few hours, but it's pretty fun few hours because you are always earning new abilities, fighting new enemies, and fighting new boss characters. Though it's not particularly my favorite style of gameplay, it's a well made game and you'll probably like it if you like cutting up robots as a ninja.