Personally I've played D&D, Das Schwarze Auge (DSA), Shadowrun 3e, CoC (mainly d20), and a bit of World of Darkness, sniffed around in GURPS and Ars Magica... and yeah, that's it.
And personally, I think the d20/OGL core engine is immensely adaptable and flexible. Happy with it. It has its flaws, but the core mechanic (d20 + Bonus vs. DC) is from my point of view not superior compared to dice pool games, just different. And depending on the exact use of the OGL (see Conan, Arcana Evolved, True20, VP/WP-Systems, Grim&Gritty, and so on), I see that d20 is flexible enough to give me my RPG fun, and frees me from learning a completely new game system. This outweighs the flaws by far.
Plus, I believe that d20 is customizable enough to cover almost everything (if tinkered enough with it).
Thanee said:
...while I enjoy other types as well, but they require a system, that is better-suited for them than d20 is.
I'm curious. I often hear that d20 is not very good in simulating certain genres, but I cannot really think of one, that wouldn't work (albeit with adapted OGL rules).