Fallout NV was rushed as fuck. FO 3 was a buggy mess too, like ALL Bethshit games, which was piss easy in vanilla as well. Unlike NV though, it was first grade retard writing, characterization, close to 0 actual C&C, no aiming, cheat VATS system, etc.. New Vegas is miles better than FO 3 and only colossal grade A retards think otherwise.
A game is meant to be fun, and Bethesda's games (Morrowind, Oblivion, Fallout 3, SKYRIM, FALLOUT 4) have sold like hotcakes. I put Skyrim and Fallout 4 in big bold letters because it is very true that a game selling well doesn't mean it is good. But if the game was that bad (as you claim) then why did people not only buy Skyrim
en masse, but also Fallout 4?
It is perfectly fair to claim a game was bad regardless of how well it did or what other people think about it, because everyone has their own set of measurements to determine a quality rating for a product. Your "bad" and my "bad" can be radically different. There's no objective measure for most aspects (you can only really objectively judge technical aspects like performance for when it comes to indisputably good things in video games, since even desired levels of considered-good things like balance can radically differ between observers).
For purchasing things
en masse, what matters most is the mass appeal and marketing, most of all. Marketing, company/brand recognition always does a large part, and I can almost guarantee you that if a game like Skyrim was released with completely identical gameplay and writing but with only altered trademarks™, by a different company with no prior history, its long-term commercial success would also differ by large. Only spectacular failures of either product or external reasons for customer base alienation can nullify the good sales effects of marketing, and similarly mass appeal can widen to the point where it's unable to grasp interest from anyone.
What is quality, then? Does a game like Dwarf Fortress, for example, with way overcomplicated simulation mechanics and complex gameplay structure have less quality than widespread success of other games which feature random generation at large? It's impossible to tell, because even 'fun' which you mentioned as the important judging aspect is subjective in people, and just because
more people find it fun, that doesn't mean it's better, but maybe just that it's simpler and majority of mainstream customers will prefer that to complexity (even if they verbally claim otherwise). Mechanics such as level scaling easily make a game more accessible and more enjoyable to the majority of playerbase that won't power-game or optimize builds, and if done reasonably (not like in Oblivion, where the level scaling is not just annoying due to its nonsense and flattening the character progression curve, but actually fucked up to the point where actual casual players will get the most fucked by it and it's counterproductive), it will lead to a game being more accessible, more casual, more fun, and sell better. That doesn't mean that it doesn't come with its share of drawbacks that can have arguments made for it for why it makes the game "worse".
Key point being, to me, for instance, a bigger insult for a game than it being just "bad" is a game being soulless, and feeling like it was made with the intention to capitalize on marketing sales trends or rip-off more popular products and their aspects, where there was no solid concept for it aside from just having it be as the intention of being a product, which, understandably, is how mainstream AAA vidya companies have to operate.