Yesterday I played Cave Story for the first time. It was pretty fun, and despite its age (13 years) was pretty great and enjoyable. For those unfamiliar (probably most of you), it's a 2D platformer/RPG where you explore an island, fight enemies with a variety of guns which level up and down as you engage in combat, and seems to have a bit of a focus on cool boss battles. The game is about 5 hours long, and I think there was something like 14 boss battles in that time, which is pretty good going. The difficulty curve is really good, with the later boss fights getting reasonably challenging, and platforming getting somewhat complex as well (especially once I got the Machine Gun, which I quickly discovered lets you hover), and save points are pretty common, so it's a fun challenge and not usually frustrating.
However, after finishing the game I discovered there is a good ending, and i just got the normal ending (I also got the bad ending along the way but fortunately that one is super easy to just load from before and keep going). Sadly, the game REALLY falls down here. I'll warn you now, there might be a few minor to moderate spoilers from here on:
* The requirements to get the good ending are really random. Don't go talk to the person who falls down a hole and gives you a useful powerup. Explore a room in the middle of a boss battle (or technically before instigating the boss) to find a specific item - that only appears if you did the previous task, which is entirely unrelated. Then continue on doing a few other specific things. The results make sense, but I don't see any way you'd work out it's what you're meant to do, unless you already knew.
* The game throws save points out of the window at the point the game gets really hard. This is the one thing that made me stop playing - up to this point, saves were frequent, there was usually one available close before and soon after every boss, as well as scattered throughout the platforming areas. But the final areas of the game on the good ending... no save points. They're also probably the hardest areas in the game, which would be fine... IF the game continued with its own establised "rules" of having saves often. They're tough, but mostly fair on their own. You have to go through three difficult areas, after which is a boss fight without any kind of explicit recovery, so most likely you're going to try and grind for some health before it, which takes a while.
All in all getting to that boss took me around ~10 minutes each time. If there was a save point here, I'd be fairly happy. You could get through that annoying grindy bit, and be ready to challenge the penultimate boss. The boss isn't too hard once you know what you're doing either, although he has a OHKO attack which will only ever get you once - but will probably get you once. And that means 10 more minutes of repeating this area, joy.
And as you might expect, after this... there's still no save point. And in case you're wondering, no checkpoints either. You go on from this area, get a recovery point, but still no saves. And then you have the final boss. I fought him once, and once I figured out his patterns he didn't seem too bad... in phase 1... out of 4... but I still died because I lost too much health as he dashed around unexpectedly in ways I wasn't yet able to anticipate.
At this point, I gave up. Not because I don't think I can do it, but because I don't want to have to play through the same area another maybe 3-5 times, taking 10+ minutes each time, just to reach the final boss and have one attempt at it, and likely get destroyed several times there in the process. It isn't fun any more, and it isn't any more challenging having to play through the same areas several times.
So, TL;DR: Cave Story is really fun. Pretend there's no good ending.