Unique, challenging, repetitive game for fans of the infamous Capcom "rating system".
Basically, the game scores you based on various factors (damage taken, number of enemies killed, time, etc.) after each room. By getting a higher score, you can buy better suits, which helps you reach even higher scores.
All of the enemies attacks are either slow-moving projectiles that can be easily dodged, or are laser beams that charge beforehand and can be easily anticipated.
The levels in this game are made up of "rooms" that are recycled again and again. Also, the game encourages you to go on "trial missions" that are randomly-generated levels made from rooms you've already been in.
Basically, this is easily the most repetitive game ever.
However, this is also one of the most skill-based games ever. None of the enemies can sneak up on you, you have no excuses for taking damage even once throughout the entire game.
All in all, an excellent game that is in a category all it's own.