It's all personal opinion to some extent, but I thought I'd comment.
Tanks
I too am over dioramas. As Dennis Wong said, stick and moss tanks. However, sometimes I see a diorama I like, and Luca's is one of those. He is a master aquascaper and, generally, I like most things he does.
As far as the Dutch, again, a lot of personal bias comes into play. I can find an issue here and there with all three of the winners, and I'm not sure which I'd put as first. Tim is a good guy, and I think he did a great job. I'm not a fan of that Fissidens part. I don't know the #2 person, and I agree with other's comments there. I like Omid's as well and feel he did a better job with the "street" leading to a focal point (the Barclaya) than any of the others. That's a requirement to me, and the others don't have it. Yeah, they have streets, but they aren't supposed to go off to random places. IMO. I have to 100% agree with the comments above about the yellow lights. It's hard to get a good depth of field, in focus, saturated pic of a tank though, and pics sometimes come out a little yellow even when the tank might not be.
I'm not as concerned with number of plant species as other people. I think a tank can look over stuffed with just a few species and perfect with what is defined with too many. Its all in how they are placed.
AGA
1. In the "Aquatic Garden" category, I wish the AGA would do away with categorizing by tank size and change to single diorama category and a single nature aquarium category without separation by size.
2. I also wish the AGA would do a "Garden Style" category for all the multi colored tanks everyone likes these days. I think Tom Barr had one of the first ones a few years ago. I called it his Pride tank because of all the colors. It was over the top. I loved it. People love these tanks and the AGA is neglecting the interest.
3. One thing I'm very happy with is the push from the AGA and people here to educate about true Dutch style as opposed to the multi colored garden style. When I see someone post a pic of a many color tank and label it "Dutch," I just cringe.