Cave Story is a sidescrolling action platformer, originally released in 2004 as a free download for PC. It was developed over five years by Japanese indie Daisuke Amaya, better known as Studio Pixel. It’s a story about caves! And rabbit-people. And robots. And dogs. And Balrog. It is not a story about a dying Japanese shoot-'em-up dev, or a spinoff of Portal 2.
(Cave Story is the sort of game that works better when you don’t know anything about it going in, which is why I don’t want to say too much about the game itself here. I also don’t recommend looking at guides or anything until you’ve finished the game at least once.)
Some backstory, to give a bit of context for why I picked Cave Story instead of a beloved classic 4X or CRPG or whatever: I’m kind of an awful person to be picking a game for the Classic Game Club, a series about PC gaming. I was completely surprised when I was picked for this session, after making a couple of short posts about how I did incredibly poorly in my first-ever game of Sid Meier’s Alpha Centauri; aside from various shareware DOS games from Apogee, id, and Epic Megagames, I didn’t really do PC gaming growing up, and most of my more recent PC experience is with games released well after the timeframe the CGC is designed around, so I already knew I was going to have a rough time picking a game. I’ve always been more of a console (and especially handheld) guy, so I never followed PC stuff during the glory days the CGC has largely covered. Even after I started having non-dial-up Internet access about a decade ago, I didn’t have anything close to current PC hardware, so I didn’t bother paying attention to new major releases, and most of my PC gaming within the CGC-relevant timeframe was limited to emulation and lightweight freeware titles. Cave Story falls into the latter category; a friend in IRC recommended it at one point almost a decade ago, and so I gave it a shot, and loved it. I hope those of you who haven’t played it yet love it as well!
As mentioned, the original PC version of Cave Story is freeware, and can be downloaded from Studio Pixel’s site (first link, near the end of the page), with a translation patch available from aeon genesis. There’s also a commercial version available on Steam (and several non-PC platforms), but it costs more than the $10 CGC price cap, and (in my opinion) has an inferior translation to the aeon genesis patch.