I find it a bit hit and miss.
You get all these people who have huge gamerscores, because theyve gone out and played alled the games where the acheivements are laughably easy to get (Such as Samurai Warriors 2, where you get all your acheivement points just by playing the game and unlocking all the other characters)
Those people bother me, because its not like they are playing and getting the acheivement to show how far they are in a game or all the extra stuff theyve done, but its more of a 'look at my score, im more hardcore' thing to them.
I think what bothers me is how differant some of them feel. It can easily range from 'That hardly felt worthy of an acheivement' to 'Do I really want to spend all that time for just a few extra points?'
Theres a few games that only require you to play for a short time before it just throws an acheivement at you, while others will have you do something that can take a such a huge amount of time (Not including acheivements for completing or getting so far into a game)
My biggest issue with it probably, is that it reveals what games you play. While some people dont mind this, it can be a problem for others, can make you wonder why none of your freinds have played game x, or if your the only one who hasnt played game y.
Add that to the fact that you only have to let a game load up for it to be listed forever in your profile, which is especially annoying when it comes to demos of the live arcade games.
I'd like it if there was a way to hide the games your played, so it only shows your score and rep, or to select games to be hidden if you never got any achievement points and/or never really bothered playing the game.
Ive actually created a 'test account' on my 360, so I can play a game for a bit to see if I like it before using my actual account to play it...