A good game if you like Diablo, but it lacks some of the originality and mood.
Nox came along a little bit later, without nearly the same marketing hype or fanbase. However, after playing the game for even five minutes you realize that in gameplay it's almost exactly the same. It's a third-person isometric view that you navigate and click on monsters/items to interact with them.
One of the things that in my mind really marked the first Diablo was the mood the game created. The dungeon/hell atmosphere punctuated by an amazingly eerie soundtrack really pulled the player into the game experience. Nox lacks this distinction, having a more traditional RPG atmosphere. However, the upside to that is that the world is not very repetitive.
To say that it's a clone, however, is not really giving it full credit. It features some line-of-sight mechanics, and a separate storyline for each profession. However, in the end of the day, the single player game is still the same idea. The multiplayer is worth taking a look at on it's own, but I'm not a multiplayer fan, so I'll leave that review to some one else.
Overall, I wouldn't advise this game to the action RPG fan of this day and age, but it served its purpose, filling in the gap until later greats, like Diablo 2 and Dungeon Siege, could improve on the genre.