I always liked the system's robustness, the feeling of actually being in total control, and its transparency: no mysterious hidden system files or random disk accessing.
But as mentioned above, the more outdated it becomes, the more patches you install to compensate, the more fiddly and flaky it all gets.
To finish on a plus and answer the original question: I like the clever modularity of it all; the elegance. Tooltypes are cool, as are datatypes, as are the startup and startup-storage directories. I mean, how simple to change stuff?