I have Shubibinman 1 and 3, but not the second game yet, unfortunately... I have played it a bit in emulation and it seems good, but I definitely want the real thing. The issue is that I'd rather have the US version since the game does have some story, but it's very expensive.
As for the two I do have, I like the first game quite a bit really, it's a pretty fun and quite challenging platform-action game. The third game, on CD, is great fun while it lasts, but it's sadly insanely easy; I beat it very quickly. The first game is a lot harder because you lose a lot of powerups when you die, meaning that if you want to win you kind of can't die at all. The best I've done so far is to get to the final boss... but then I died, and while you can technically continue, in reality it was hopeless because of the loss of powerups and health. I like the branching level tree, also. The choices, and number of levels, is great; even if there are only a handful of different visual themes for levels, there are a good number of different actual stages. Shubibinman 1 is a lot of fun and I quite like it.
Of course the third game has more polished gameplay and much better visuals, but with its seriously lacking challenge and short length I don't know if it's as much better compared to the first one as most people say. Yeah, it looks good, has some cool scenarios along the way, has CD audio music, cutscenes instead of just text boxes, has some gameplay variety, and more... but it's over almost before it begins! What happened to the challenge of the first game, there is almost none. Too many of the levels are just linear corridors, too -- 3 has almost no jumping puzzles outside of maybe two segments, and that is unfortunate and hurts the game a bit. The first game has plenty of jumping-puzzle segments, why are they almost entirely absent in 3? This kind of game is better with them. The third game is entirely linear too, with none of the first games' branching paths, and doesn't have the shops to buy items from either, just regular powerups. I have nothing against a strong linear experience, but the first game probably has more content, and I do like the powerup store and alternate routes even if they aren't essential. So, overall, as fun as 3 is, I like the first game more. I think the first Shubibinman is quite under-rated, it's a good game.
Isn't the second game a bit more shooting-focused, though? In the first and third games, really the sword is your main weapon most of the time.
