OS 4.1 is the best O/S I've ever used. At all. And I've used a few (including AmigaOS 1.2 through to 3.9 and 4.0).
Why? Because it's very very fast and responsive, isn't full of bells and whistles that lower reliability and speed, it's intuitive to program (pardon the pun) and it's just NICE. It does all I need an OS to do, and doesn't pretend to be something it isn't (c.f. Windows pretending to be some kind of media hub or something). Backward compatilibity is also pretty good and runs most things I've thrown at it.
OK, it's not as solid as a proper UN*X system, but it gets a darn sight more bang/buck because of it, and that's how I like it. It's a cost of the Amiga-style memory system.
