Again...this is a personal preference thing. But I disagree with you when you say that people are suddenly coming out of nowhere to criticise the sixth generation - the criticisms have been there for years, and plenty of people have had them.
The most obvious and frequently voiced criticism - before the games were even released officially - is the number of Pokemon in the sixth gen. As with every generation, design mileage varies depending on what you like in your Pokemon designs, but the number is generally regarded as an issue in that it was smaller than every other generation prior to that and felt like a step backwards from the fifth generation, which inundated us with an entirely new Pokedex. XY went the other way - it saturated us with old Pokemon and gave us very few new ones; the opposite extreme end of the scale. In some ways that is better, and in others its worse. Quality over quantity? I suppose that depends on what you think of the quality.
X/Y also continued the trend with poor NPC integration and development into a lackluster plot that we'd seen dozens of times over already. I already went into that extensively in another thread so I won't do so again here, other than to say that X/Y were much, much worse with this than either of the fifth generation titles, saddling you with a group of "friends" from the get-go and forcing a good part of the game to go at a snail's pace. The variety of designs in the characters was fantastic...unfortunately, they forgot to give any of them personalities.
A personal one for me is the models replacing the sprites; they look like washed-out plasticine. They're not as vibrant or well-designed as the sprites of the fourth generation, and they in no way push the 3DS to its limits the way the fifth generation's rather disastrous sprites did for the DS. I was very let down by the visuals in the sixth generation games in general...and in light of the seventh generation, this is only more appearent, given the improved character models and more vibrant locales. Combined with the lack of postgame, these felt like beta test titles, rather than full Pokemon experiences. At least to me.
And that lack of a proper postgame is a HUGE issue. So too, in fact, that we haven't had another title revisiting Kalos by this point. I suspect a lot of the complaints come from the fact that the region feels unexplored and unfinished - a stop-gap, if you will, between Unova and Alola. You could forgive the poor quality of XY if the much yearned for Z had been released after ORAS and expanded upon the region, offering a more complete story and some postgame content. Kalos, however, has been abandoned entirely, it seems. This isn't going to sit well with people, especially given the positive reception for Sun and Moon, which are generally regarded as the best Pokemon titles in years. I personally don't agree with that, but...well, look at the sales, amongst other things. These things only serve to highlight just how little thought actually went into XY.
A lot of people complain the games are too easy due to the EXP Share mechanics being changed, but I just don't agree with that. For one, you don't have to use the EXP Share at all. For two, people who make that complaint have been playing Pokemon for years and will know how to manipulate the systems to their advantage. For three, Pokemon has always been easy; these are games that are designed to be played by anyone, so difficulty cannot be a huge factor. Fans have always been capable of providing their own challenge in Pokemon titles, and should know what to expect by now. Granted, B2/W2 had Challenge Mode, but the method of unlocking that was unnecessary convoluted and generally made it impractical for a first run-through, so I wouldn't really use that as a point. But that's just me.
ORAS I found phenomenally disappointing, primarily because I feel that they should have remade Emerald. I played Alpha Sapphire and, improvements in visuals etc. aside, I felt like I was getting half a game. I had this with Ruby and Sapphire, too - in focusing on one evil team, they left the other out entirely, but they were still present and active. Half the plot was missing. Emerald, which incorporated both teams, was a complete experience. A lot of people were annoyed by the lack of customisation in ORAS too, something that was regarded as one of XY's more positive aspects and was generally well received. Removing that was a slap in the face...and, in light of the feature being added back into Sun and Moon, it shows how unnecessary it was to remove it in the first place.
...that said (since I feel I have to be slightly positive) I think the sixth gen titles deserve praise for the simplicity of the online features. B/W/B2/W2 had a terrible online interface, and Sun/Moon have made the entire thing irritatingly and unnecessarily convoluted. X/Y and ORAS had a very simple, easy to navigate touch-screen based menu you could access within minutes. It also introduced fun things like Wonder Trade. The sixth generation also started to make competitive battling and breeding more accessible and less time-consuming with things like Super Training and improved breeding mechanics. A lot of people argue that the old ways were fine, but...options. It's always nice to have options, and a feature dedicated solely to EV training that requires no real instruction to use and is available from the beginning is a pretty good one...and, again, you don't HAVE to use it.
Time changes perspectives and, with Sun and Moon being obscenely popular, I suppose some people have changed their outlook on Gen VI...much the same way people will look back on Gen V or IV and realise they weren't as good as they initially thought. But the criticisms, and the problems, have always been there.
As for the anime...a lot of people are very salty over the way the XY anime ended, and can you really blame them? The anime defied all expectations and buildup by having Ash lose the league to Alain, there was no real resolution with Serena's crush - which in itself was a pretty surprising thing - and the show pulled all kinds of inconsistent crap with Ash-Greninja, etc. The anime failed to deliver on so many levels it was unbelievable and, after the Unova arc was generally frowned upon, it felt like a return to form. At least, that's the sense I've had from it.
