Yes, I registered to post this. No I'm not OP. Nichtsdestoweniger, I'm going to have to agree with OP. I played Fallout 3 for about 48 hours, subtracting a good 20 for sleep, food, and a class or two (this was last Halloween. I skipped Franklin St. for F3. Damn.) and I got just about every achievement, found damn near everything, (when I went to sleep, all I had left was the last little push in the Main Quest), and had rather thoroughly enjoyed myself. But, as much fun as the game was, it was, indeed, rather short.
Ok, I started another character, ignored sane skill/perk choices for cool sounding ones (Child at Heart + Little Lamplight = the most disappointing 10 minutes of November, including the trip there), and had myself a merry 150 (and still going) hours. Further, I'm all kinds of excited about Bethesda's secondary development team, the modding community (the folks who finish their games for them...).
But, as for the game Beth shipped, and the way I played it at first (y'know, selecting perks I thought would be useful, and not wasting time where I figured my character wouldn't), it was shamefully short, pointlessly easy, and worthy only because of how entertained I was during what little time I spent in D.C.