I'm not denying the validity of these points, they definitely have truth behind them.
I feel Fallout 3 isn't really supposed to be a serious, gritty game. The main story may feel like that's what it attempts to do, but it feels like they didn't go after a very serious tone, making the first moral choice seem fitting. Moira seems to be a great example of this with her stupidity and airy "dumb-blonde" voice. The complete silly moments like the pint sized slasher and little lamplight, I don't remember FO3 for a riveting story and immersive gameplay, I remember it for being fun. New Vegas does mix this up a bit and makes it a bit more serious, while still being fun.
It's definitely not what some people want out of a Fallout, so I of course understand why someone might not enjoy this game as much, but I found it to be an enjoyable experience with memorable moments.