I think I spent ~30h on ME1 and ~25-something on ME2.
40 hours for ME3? Nice!
I've played a bunch of JRPGs that offer ~60-70 hours on the first playthrough alone - don't forget NG+ -, and while they're filled with awesome content, my attention span sometimes fails to hold out. 40 hours might actually be the sweet spot.
Regarding the difficulty - whatever floats your boat. Some just want to enjoy the story and thus drop the difficulty down a notch. Others enjoy the gameplay aspects. I personally think the AI is often too poorly done to be worth the frustration of a higher difficulty setting. I often just end up lowering the difficulty(if possible), or exploiting the bugs/glitches/holes in the enemies' behaviour...
Especially if the enemies themselves exploit the glitches, the cheap bastards (Yes, I'm looking at you, Jagged Alliance BIA
)Edited by Hyoketsu - 2/27/12 at 10:16am