Honestly my probably biggest complaint would be the lack of development in the towns as many people say. They needed to be more fleshed out.
How ever reading through the thread there are other problems, this i know of course. Some people pointed out very unique things though. I think @InnocentClarke pointed out some of the most interesting things to me being how the game handled some its wasteland politics and Religion. I think the main good behind the NCR was it's people and a handful of the military leaders we meet. Other than that the NCR only seems better because the Legion is just so terrible. Religion as aforementioned is all but non existent. I think only one NCR trooper in all the wasteland hints that people still practice Christianity back in the NCR. Other than that there is a distinct lack of churches or religious organisations.
While i'm almost certainly in the minority on this i was actually pretty alright with the lack of enemies in the wasteland. I always thought it was a problem personally that there were so many enemy encampments in FO3 and FO4. I think groups like the fiends could have been spread out a little more, but overall i like they had their area of the game which makes sense since they have a homebase. Their arsenal on the other hand certainly could have used improving, while they had a decent selection of weapons their armor was lacking. However prior to some of the original updates they were always more than a match for NCR troopers. I don't know how many people remember but fiends use to shred NCR troopers around MCcarran. Other groups like the Vipers and Jackals could've used a few named NPC's and quests tied to the wasteland towns in the south side of the map.

Maybe the best way to ask this question, here in the year 2018, is criticisms of New Vegas even with mods.
It gets much harder to criticize when mods are used, that fix so many of the original short-comings. I find myself saying "Well, this is good but could still be better," rather than "I hate this aspect of NV even with mods."
There's not a lot to truly hate in NV, here in 2018, especially if you don't need completely modern graphics (I suspect that no amount of modding in NV can recreate some of the vistas I've seen in a modded fallout 4 or witcher 3.)

I think it's incredibly lazy that 99% of the plot is ripped straight from Van Buren, characters and all. This doesn't mean the story is bad, in fact it is extremely good; it's just simply lazy that they didn't do something new (although I guess they can't really be blamed considering they had like 18 months to write a story AND make the game.)

You're upset that Chris Avellone was finally able to give us much of fallout 3 that he had originally wanted to make?

@Sirdanest wrote:

You're upset that Chris Avellone was finally able to give us much of fallout 3 that he had originally wanted to make?  

You're misinterpreting my words, I said it was lazy, not that it wasn't a nice thing.

I wish obsidian negotiated for a longer dead-line, this game could have used some improvements.