People hate on Amelia for being boring(probably the same people who hate on Lisa for no reason) which I guess is a fair argument. Supernatural does not treat it's female characters fairly. But have you considered that the whole point of Samelia(and Deanlisa for that matter) is that Sam tried to have his apple pie life and it didn't work? Even if they had put real effort into Amelia's character, that wasn't the point of the plot.

I think it's also that people get mad at Sam for not looking for Dean in purgatory. As if he was supposed to magically know. As if Dean doesn't tell him 200 times "If I die, don't look for me. Go live a normal life and be happy." (It's one thing for Dean to be bitter, considering HE was the one stuck there, but it's not a fair critique of Sam).

ALSO Samelia is an important turning point for Sam's character. It's when he really truly realizes that he'll NEVER get a normal life. That though he wanted it for so long, it's not going to happen. Because hunting got more complicated. Because he changed. And it just wasn't something he was able to do anymore. After Amelia is when Sam starts saying he doesn't want a normal life, partially because he starts to understand that it's hopeless.