It was . . . okay. The number of cycles it actually took to do a lightweight message pass was dismaying, though. The newt would have benefited from a less partitioned design for the underlying page and storage management.

I used another microkernel OS on a set-top box. Now that was a misery, but one I attribute more to the uncaring attitude of the company that wrote the STB's firmware than any inherent problem with their OS (a decade later, critical and customer-affecting race conditions are still present in their code). To be honest, their OS didn't help.

I don't think microkernels are bad. Making bad choices about performance that affect performance, battery life and other things that customers care about is bad, and you might have to break some abstractions in your microkernel to address those.