I absolutely love Shadowrun.. although I've seen games here before in the past that jaded me.
It also really depends if you're going rules heavy or rules lite. The nature of play by post really hinders a rules-heavy game.. like SR or SpaceMaster.
Plus..lots of differnet people have different 'power levels' in mind.. the characters I saw proposed .. well.. as a GM I'd never have allowed
But I like to play the grittier 'starting out shadowrunners against the world' not the 'elite combat force who could take on mega-corps or small nations in their own backyard'
I'm most familiar with 2nd and 3rd edition.
Say..anyone notice how car's nowadays are looking more and more like Shadowrun cars?