Ib is perhaps the most popular game out of the three I've listed. People still make fanart of the characters from time to time, which is something I can't say the same for the other games. It is much more character-based than either The Witch's House or Mad Father, which certainly has something to do with that mode of engagement with it.
The surrealism of Ib is the first thing many point to as its strong point, and I have to say that I completely agree--it takes place in an art museum, after all, and chronicles the thoughts of a very troubled artist. Therefore, most aspects of the game attempt to capture the scrambled, disturbing state of that artists' mind through a combination of established horror imagery and more symbolic, uncanny, and unsettling tones. Sound and music--or, sometimes, a lack thereof--play an instrumental (hah) role in cultivating this aesthetic.
For many, this game served as an introduction to RPGMAKER horror, and I believe it is quite a good one. It showcases very effective use of some of the hallmarks of the genre; solid and unique characterization, puzzles, unsettling atmosphere, expected-but-not jumpscares, and a female protagonist, to name a few. Not many games in this category have deviated from these elements. This isn't meant to imply that Ib was the first game to do this, as it almost certainly wasn't, but it is one of the best versions of it by far. Most other RPGMAKER horror games cannot compare.
