What effect does an xbox player review have on the reviewed player - does their rep or gamerscore change? Do they see the submitted review?
A person's rep is somehow affected by player reviews (except where noted in the player review - for instance, avoiding someone due to their skill does not effect rep), although the exact algorithm is very unclear.
Wikipedia says that if you've got no reputation, but then you get a 'preferred' from at least one player, your rep will eventually default to 5 stars. One assumes that a chain of negative player reviews will, over time, decrease this star count. I've had only a couple of positive reviews and several negative ones (apparently I "trash talk" from time to time!) but my rep has stayed steady at 5 stars for as long as I've been interested in checking.
You can see the feedback you've gotten from others, broken down into percentages, from your profile. I can't find a place this is given on the Xbox website, but you can get to your profile from the furthest right "slice" in the Xbox Guide menu.
Player reviews also are taken into account when in multiplayer matchmaking, although avoiding a player is not always enough to ensure that you'll never be matched with them again in the future. I believe this is just one aspect of a much larger algorithm used for matchmaking.
There's no gamerscore impact for reputation, and note that submitting a player review and/or a player's reputation is a separate system from filing a complaint. The complaint system is the system that can lead to suspensions and so forth. It is intended for abusive players or those who are glitching or hacking their Xboxes.
Player reviews/complaints affect the player itself if anything.
If you have a complaint against another player, depending on what they did, and the consequences of the so called offense, it can potentially threaten the Xbox Live account itself.
Player reputation will be effected depending on how many people avoid, or prefer the player. This can be found inside your account section/reputation.
Gamerscore is never effected during any of the above. If your account is banned, then basically your Gamerscore is gone as well until you get your account resolved.
Source: Xbox Live FAQ, and personal experience.