For example: the Fatman in Fallout 3.
Spoiler
You can take the Fatman from a dead body as you reach the Galaxy News Radio station. This was absurd. Such a powerful weapon shouldn't be received so easily, and even at low levels with no challenge. The reason Bethesda did this, was to wow people by quickly destroying the super mutant behemoth with a nuclear blast. I believe it would have been more satisfying to take it down with the other weapons you had, and with the combined effort of you and the soldiers.
The other problem with this is, is that by easily obtaining the Fatman, you don't feel any sense of achievement. You also value it less. I'm all for having unique, hand-placed items spread through the world, but when there's no challenge in obtaining such great items, the experience is cheapened.
Fallout: New Vegas remedied this problem I think. My character is leveled somewhere in the 20s, and I haven't found the Fatman yet, and I've only found one mini-nuke. There's only fourteen mini-nukes in New Vegas. Compare that with seventy mini-nukes in Fallout 3 that can be obtained relatively easily. Having so many of these mini-nukes in FO3 also cheapens the experience. They're supposed to be very rare, and difficult to get. Much like how Daedric armor was difficult to obtain in Morrowind.
So Bethesda, I really hoped you've learned this. Your thoughts?