I played Legend of Grimrock from front to back. It's a pure nostalgia trip, extremely well done, and I enjoyed it immensely. If you like role-playing games of the retro school, I recommend it.
Once again, Legend of Grimrock is a ton of fun, and I enjoyed it immensely. However, it is a game on a square grid with monsters, pressure plates, secret door switches, and holes in the wall that shoot stuff out. There is only a limited number of ways that you can piece those elements together to make interesting dungeons for the player to explore. It's finite, and, by the time I was at the bottom of the dungeon, I was already noticing elements repeating themselves.
As I said, there might be a Grimrock 2. But, as we discovered twenty years ago, this earth will only stay fertile for so long before it needs to lie fallow again. Only then will it yield a fresh crop for a new generation of gamers. (Analogy!!!)
This is NOT a criticism of Legend of Grimrock, which is, for the third time, very good. This game doesn't have to be responsible for carrying future titles. It only has to be fun by itself, and it does so very well.
I just think it's a good example of the varying durability of different designs. Some can support many titles. Some only a few. This isn't a problem. It is simply important, when planning games beyond the first, not to heap onto a humble structure too many expectations.