We've had review/reputation systems in the past, and have examined & reviewed their use on other boards. We don't like the endgame.
If we were to agree on something we think would
would well, designing and implementing it would be a large investment of time and energy that's not only better spent elsewhere, but doesn't have a return that justifies the investment.
Our general rule is not to enact any policy that'd hinder creating or playing in games, or create undue discrimination in GM or Player selection.
It's why we don't have post count listed next to your name on every post. Post count, even post rate, are not useful statistics, because neither tells you if someone ever drops off the face of the earth and returns, or why.
It's why we don't strictly require someone to be a 'Game Member' to post - it's extra hoops to jump through in order to get things moving, and that discourages people. Games dying also discourages people, but I'd rather they got to play, even for a week, first. That, though, is a discussion we've had time and time again, and I'd rather not return to.
All that aside, I think general wisdom right now is that upvote/downvote is a lot more effective than a rating scale, especially one like 1 to 5 where there is a direct middle ground (1 to 4 is better).