What each of us need in styles varies dramatically. A lot depends on skill level (if you don't play much, your arranger needs to play more), a lot depends on what you use it for (if you mostly sing, and use the arranger for accompaniment, you need a different level of playing density to if you are playing a lot yourself), etc., etc..

What works perfectly for one is a busy mush for another. Arrangers are, in a way, just like bands... some overplay, some underplay, some get it just right, but only when they are backing one particular frontman.

Personally, I think style density (not just how many parts are playing, but how busy each one is) is probably one of the MOST important considerations when it comes to deciding whether you like an arranger or not. Forget the sounds, forget the OS... Do the ROM styles leave JUST the right amount of space for how YOU like to play? Get that wrong, and it doesn't matter too much whether the sounds are great, or the panel layout is perfect or not...

Just a thought...