What bad treatment did Bethesda give past games?
Last I checked, Bethesda developed games are 3 for 3 making "greatest game of all time" candidates (Morrowind, Oblivion, Fallout 3) and even for those who don't share my opinion that they are the "greatest games of all time", all 3 of those games were huge mainstream successes and critically acclaimed games.
New Vegas would have gotten more critical acclaim than Fallout 3 if it had a few less bugs and game critics are open-minded enough to realize COD isn't the definition of gaming. NV sold more copies than FO3, btw.
New Vegas improves upon everything Fallout 3 lacked, good story, good writing, great characters, weapons that were not wet-noodles, more weapons, insane amount of crafting choices from ammo types to exotic weapon binding ritual to crafting super deadly explosives to making food that heals you in a nanosecond for a long time to tanning gecko hides under a campfire, fewer and more powerful perks that help you roleplay and not just add points to your skills, and traits.
Fallout 3 is still a great game, though.