I loved Fallout 3. I have probably played through it 3 or 4 times completely. I also have all of the add-on packs for it. I occasionally had a couple issues while playing - usually just freezing of my PS3 though. The game was mostly stable.
New Vegas on the other hand seems to have an issue or two still, even after an update for it already. So far I've found what appear to be two major bugs and have also had it freeze up on me twice.
NOTE: Possible spoilers ahead.
The first bug was when I was going to meet Caesar in his camp. I had both Rex and Veronica as companions and had to take the barge across the Colorado to his camp. Apparently at acme point in the barge ride, Rex decided to go for a swim or disappear. So when I got to Caesar's tent and had to enter alone, he was nowhere to be found to tell to stay put. So it was not possible to enter the tent. It was also not possible to leave his camp without speaking with Caesar. So I was basically screwed. Thankfully, I was able to load my last save which wasn't too far back and then tell both companions to wait at the dock before getting on the barge. But if my save were much further back, I'd be kind of pissed.
The second apparent bug came just the other day when I was trying to go back to the strip. Keep in mind that I have been in and out of the strip many, many times already via Freeside. The Monorail at McCarren had already been blown up. So imagine my surprise when I try to go to the strip again and the Freeside gate tells me I need a key. No idea why... I didn't drop or sell anything that I thought I needed.
I have no solution for this one yet. I have not yet played again since I encountered that, so I'm not sure if maybe a reload will fix it. I hope so, otherwise I'm not getting back in the strip again. And that's a bit fucked up.