I didn't forget a thing. I replayed TW2 recently right before playing TW3. The rain in Flotsam doesn't even compare to the thunderstorm I saw in TW3.
And saying the environments in TW2 are almost the same as TW3 is laughable at best. The most open area in TW2 that came the closest to TW3's areas was Aedern and if you compare Aedern to White Orchid, well, White Orchid is way bigger, it looks better, it looks more interesting and it has more details and more stuff going on.
TW3 also has better lighting, though admittedly TW3 looks at its worst during a clear midday, it definitely lacks atmosphere then, but to be honest, real-life looks boring and not that atmospheric during a clear midday too, so I suppose it's actually quite realistic.
The water in TW3 also looks quite amazing as it is, I don't get why anyone would complain about that. It's perhaps the best water I've seen in any game so far.
But what really makes TW3 shine and much more beautiful than TW2 is all the little details that brings the game to life, details that TW2 didn't have, such as a big variety of weather effects, including very impressive thunderstorms with lighting that looks most amazing during the night, windy days that make all the foliage and trees move and shake realistically and rain that looks better than the rain in TW2. Or details such as Geralt's beard growing back after he shaved, or all the little blood vessels that show up on his face after taking a bunch of potions, it's stuff like this that makes me smile from ear to ear when I play TW3 and discover these tiny details.
As for the downgrade: I seriously think people should stop complaining about it. The game looks amazing as it is and I doubt anyone could have ran the "original version" of TW3, unless you're running two GTX 980's in SLI or something. I personally run the game on a GTX 970 and I actually had to turn off Nvidia Hairworks and set the shadows and foilage to 'high' to make the game run at a solid constant 60FPS (everything else on 'ultra'). I'm happy with the game as it is.
And finally, if you think stuff like ENBs aren't taxing on your system then you seriously have never played Skyrim with a good-looking ENB.
PS: Overused bloom is ugly as hell, I'm happy TW3 doesn't go crazy with the bloom.