Shoot-em-up style games were already a pretty well known genre well before the NES hit the scene, and it continued to get quite a few throughout its life, with a lot of them being unremarkable ports of arcade games with pretty basic gameplay and minimal variation, so I tend to glance over a lot of them. Sqoon is a relatively early one for the NES, but its design is anything but basic - there's quite a lot of mechanics that you'll have to juggle to get far. There are the usual waves of giant enemies to blast away for points, but other sea life appears too - orcas are harmless to you, but will eat up any people you blast free by bombing buildings, crabs drop gold bricks you can collect and turn in for points, and the odd sea slug will drop a magical necklace if you bomb it enough times, which grants a 1-up and a chance at a bonus stage. In between all of this, you'll have to free captured humans, touch them to bring them aboard, and once you have nine of them, drop them off on the "floating island" that appears (one by one, with the B button), which is the only way to replenish your constantly dwindling oxygen supply and gain powerups to upgrade your weapons. The aforementioned gold serves as a more efficient means of doing this - all you need is one live human and a gold brick to get the island to appear again, though this will only refill your oxygen and not upgrade your weapons (which makes it a better option when you've already hit max upgrade). Sqoon is chaotic and outlandish even by shmup standards, but undeniably unique and quite a lot of fun once you get into the swing of it.