I think people are remembering TW1 with rose-tinted glasses. Or, well, murky ones.
TW1 had its share of melancholy atmosphere, but it also had a good amount of colorful places. Chapter 1, arguably the most gloomy of them all, was balanced by Chapter 4, which was just full of peaceful fields and a picturesque village. Vizima's temple quarter wasn't the most merry one, but the trade quarter felt like a festival on the other hand. Chapter 5 had a dirty civil war, but the Epilogue took place in a very bright and "High-Fantasy"ish inner-world covered in snow.
Kaer Morhen in TW1 doesn't look all that morbid all the time,
...and isn't different in TW3,
And as we've already seen in Wild Hunt, it can look remarkably dismal,
If anything, the difference in the last two images, when taken of the
same place, is testimony to how advanced CDPR's weather system is and how the same place can feel completely different based on the day's mood.
From what little gameplay we've seen so far, then, like in TW1, it has its murky parts, it has its happy ones. Johnny's swamp, Gran's house and surrounding area, they were pretty despondent. I'll also add that Damien said in his Q&A session in Russia that the way the built the map is by breaking it down to different regions, and giving each one its theme. I find that a great approach, and I expect that we'll have parts that are heavy in atmosphere and others which are light-hearted. The balance is good, and in line with what they did in TW1.
