I found their dungeon terrain superb, but their prices made it untenable for me. I invested in printable 2D tiles, printing them on regular paper, covering them with clear Contact Paper (shelf liner vinyl, translucent), then I applied them to the glue side of peel-n-stick vinyl floor tiles. I cut them to shape, and they work superbly, for a fraction of the cost…
Then I discovered how much work they are to employ within a game; I discovered how they transform the RPG into a miniatures-based game; I learned how much this slows my games down, narrowly focusing it to the limited scope of a mini's game, drastically altering the dynamic flow of my RPG game sessions, for me, and my players.
Don't get me wrong, I enjoy a good dungeon crawl, on occasion, but that is not my preferred style and approach to gaming. My players love my more open-ended style, with the occasional dungeon crawl.
I also love a good miniatures game -- I love 2e BattleSystem and 2e BattleSystem Skirmish! I just do not combine the two gaming interests very often. Not all of my players enjoy both types of gaming.
The DF terrain is superb, the gold standard, as it were. However, I find it too pricey, too heavy, too slow to use often. They would disrupt the flow of my games (wilderness, castle, city), except when I am running a dungeon crawl (see cost and time/effort concerns, above).
Having tried the various options, I have found, along with my players, that vinyl mats and markers work superbly, without the time/effort investments required by 2d and 3D terrain setups. I still do full 2D and 3D setups for one-off games. I just can't justify DF terrain for such infrequent uses. Cheers!