I own copies of:
- Dire Tombs
- Arcane Corridors
- Ruins of the Wild
- Lost Caverns of the Undermountain
Arcane Corridors and Dire Tombs work well together. Of the two, I think I prefer Arcane Corridors. The tiles in AC are brighter, however, there's more theme-y crap in AC, as it's geared toward "magical" dungeons. Dire Tombs is more basic.
I found Ruins of the Wild disappointing. The set just isn't big enough to satisfy the needs of most wilderness encounters, so you have to buy two or three sets. The set fails to provide a lot of valuable terrain, like cliffs, rocky bluffs or even basic forestry. Meanwhile, a large tile is devoted to a campground with two tents, when seperate tent tiles would have been more appropriate. The there's other crap, like a horse and buggy, which I personally think is better represented with minis.
I have mixed feelings about Lost Caverns of the Underdark. It was smartly designed with small tiles which you put together to create lots of unique caverns. But at the same time, it can be a bit unwieldy because there are some many small tiles. Also, the cavern art is very dark, and the seperation between walls and caverns is not very clear in low indoor light.
Thats my take.