I don't understand all of the praise for Fallout 3. The story and art were both excellent, yes, but the gameplay just wasn't fun. In their quest for realism, ammo was just too hard too find, and the monsters each took so much of it that I ended up avoiding fights just to save it up. I agree that ammo can't be limitless, but if you spend most of the game hunting for it, it's not a very good game.
Needless to say, I gave on that game quickly. I'd rather be having fun.
I had the exact opposite experience playing through the game, maybe right at the beginning ammo was a bit scarce for select weapons, but after a few hours in I don't think I ever ran out for my main weapons. If anything I think they were too liberal with the ammo, you can find it everywhere. It was also weightless so you never had to make any tough decisions about weapons to carry based on ammo weight. By the end of the game I was packing round 3,000 rounds for my assault rifle alone. I'm very much an explorer gamer type though, I'll double back across areas just to make sure I have explored every nook and cranny.
Only monsters that could really take a hit, in my play through, were the Deathclaws, but I found killing them easy enough as well. The big robots were also pretty tough, but 3 pulse grenades was always enough to put them down.