Screwtype, have you read the books?

The first problem is that it just didn't look like an inhabited world. It looked exactly like what it was - empty NZ landscape, interesting enough from a tourist POV, but not really evocative of Middle Earth.

Most of Middle Earth WAS empty! Or rather, most of the lands that the characters passed through were empty. Particularly in the Fellowship. But in the Two towers, Rohan had been evacuated, and the lands Frodo and Sam passed through were particularly desolate. I don't think ANY encounter between the characters in the books was left out of the movies.

The second problem is that the climate and the weather didn't reflect the action. It all just looked very temperate and nice, neither too hot nor too cold. It was fine to have sunny weather at the start, but from Weathertop on the weather should have better reflected what the characters were going through. Overcast skies, threatening weather, or at other times, parched, heated landscapes - something to create the right atmosphere.
I don't seem to remember the weather being that much of a factor in the books. They leave the shire in the spring or summer, IIRC, and by the time winter rolls around, they're in Gondor, which is much further South and I don't believe has a very harsh winter.

Helm's Deep I agree was a little murky in places, but the real problem of that battle for me is that it simply wasn't "epic" enough. It looked like no more than a few hundred orcs making a nuisance of themselves. It's a long time since I read the books, but I seem to recall descriptions of vast enemy hordes covering the entire landscape. The cavalry rescue at Helm's Deep also looked too small.
Helm's deep wasn't an "epic" battle. It was a few hundred humans against a few thousand orcs. That's it. The battles of Pelenor Fields and the Fields of Celebrant were much more massive in scope. I won't say that he captured the feeling of the Helm's deep attack perfectly (I was incredibly annoyed by the presence of the elves), but it was ok. The cavalry rescue at the end I particularly disliked, but only from an asthetic standpoint.

IMO the lack of an "epic" quality inflicts most of the action, one never really gets a sense of an entire world under threat from a vast malevolent force, rather it feels more like a little stoush between a couple of minor tribes.
I'm not sure how you're qualified to say this if you haven't seen the third movie. There were no massive conflicts in either the first two books or movies. The assault on Helm's deep was relatively minor in the grand scheme of things. If you had bothered to watch the third movie, I would agree that Gondor got the shaft in terms of being represented as a massive collection of different cultures (eveyone simply wore the same armor). But on the "evil" side, I think Jackson represented the Haradrim, the Coursairs, and of course the Orcs rather well. There is only one paragraph in RotK that mentions other races being involved on the side of evil, and not much of a description of exactly what he was talking about.

The Easterlings were mentioned much later as attacking Dale, of which the movies make no mention. But as I said before, the third movie was already 3 1/2 hours long. He had to cut something.

I realize I'm not going to convince you to like the movies, but by the same token, I think Jackson got the landscape and the sense of "grandeur" pretty much bang on. It was the tacked on bullcrap scenes that he added from outside the books that fell off the mark for me.