I'm currently in the middle of chapter 2. One of the biggest things that has jumped out at me while I have been playing it is that the humor is a lot less subtle than I remember it being in Earthbound. It seems like Mother 3 delivers a lot of it through dialog instead of the world itself, which I guess makes sense considering the increased role of the story in this game.
I think that most of the impact of the mother's death came from the way that it was delivered. The title of the chapter foreshadowed someone's death, and when they only found Lucas and Claus it was basically a done deal. But the way you got the news was shocking. It's like:
"well the good news is that I found this awesome new weapon you can use."
"alright."
"Oh, and it was sticking out of your wife's bleeding chest"
"WTF"
Also, so far I am not terribly fond of the battle system, just because it is lacking a lot of complexity up to this point. It seems to just be boiling down to attack, attack, eat beef jerky, and attack. The whole rhythm thing is not explained well at all either and so far I have only been able to do 2 hit combos out of luck. I am sure this aspect will get better, seeing how chapter 2 starts making special moves necessary to beat certain enemies and it is also pretty early in the game.