An experienced GM can probably give you the basics that you need in a few minutes. Once you understand what you can do in a system, you have a lot more possibilities, and (to a degree) the ability to build a 'more powerful' (or at least a better optimised) character. The actual mechanics of a system don't need to matter that much for a new player, as the GM can tell you what to roll and when, as necessary. I think getting a feel for the setting, and how well the type of character you want to play fits into the setting, is as important. When you have a setting with a large, well established world (Exalted, for example) or one where a fairly different mindset is required (L5R) then the mechanics (to my mind) take second place.