Xexyz (1990)

Despite the lack of thought given to the title, Xexyz remains an underrated cult classic for the NES. Developer Atlus nimbly combines platforming, non-linear exploration, and shoot-em-up for a wholly unique adventure. Xexyz spends its time in two modes: One is on foot, which plays like a Contra style run-and-gun and a second in the air which plays like a much more conventional shoot-'em-up. While on foot, the main character can enter doors in the background and find NPCs (and occasionally hidden bosses) that will provide extra story details or will sell stronger weapons and healing items in exchange for the game's "ball" currency. Each stage ends with a boss that needs to be fought in the shoot-'em-up phase. After which an additional shoot-'em-up stage carries the main character to the next world. What makes Xexyz much more than the sum of its parts is the seamless blending of all its elements; Atlus didn't just mesh a shoot-em-up with a platformer and call it a day. With all of its doors, crazy cast of helpful characters, and abundance of enemies, the islands really do feel like lived-in worlds that are under attack by an invading alien force. The castles also reflect the enemy. They're cold and sterile and must be navigated in a precise manner, lest you get lost and confused. Traveling further into the castle requires a ship, but you don't just magically appear in the ship. You enter a hangar, jump in, fly through the castle, enter another hangar, jump out of the ship, and move further. Some might call this a needless detail, but it fits with the game's thorough execution. Once you destroy the boss of the castle, your escape - another ship - is provided by the queen. You journey to the next island, fight legions of enemies and another boss before you finally arrive and do it all over again. The sequence of the game's stages flows beautifully together.