The main concept is fine but the game lacks in so many areas, that its hard to recommend
The idea to make a Diablo inspired game in future London, with demons spawning everywhere could've been fun, but somewhere in the development of the game the developers must've lost sight of the idea, because the game is uneven at so many levels, that even the core gameplay lacks the finesse, balance and addictiveness of the Diablo games.
Add to this a disappointing story. I remember the HD video / trailer (which is the starting video), which impressed me long time before the final release - unfortunately the trailer is the highpoint of the story, and the storytelling gets much worse later on. It is as if the developers had no idea whether or not the game should be funny, weird or dark. The result is just a mess inbetween.
It doesn't help that the ingame NPCs doesn't do much to guide you through the world, let alone give you an idea of the story behind it all. The missions range from silly point a to b missions, to more complex, but still not well written mission. There are a few exceptions, but basically the missions seems a bit loose and lacks inspiration or originality.
It doesn't help that clicking on NPCs makes them talk some random gibberish in high english, but at the same time you're presented with the usual dialogue tree, in text, which has nothing to do with lines the NPC just spoke. Weird design choice.
Another less fortunate design choice is the lack of different environments. In the first 3-4 hours of play, you'll probably see most of the areas (or at least the area designs) the game has to offer. Adding to the repetiveness of the game. This, of course, adds to the feeling of not getting anywhere. Progression is mostly felt through character advancement.
And character advancement has some flaws as well. Progress, especially in the beginning, is rather slow. So you'll have to wait for the fun skills - and those are far and few between. To put it mildly - many of the skills feel unnecessary or underpowered, let alone uninspired.
Does this mean the game is bad?
Not really. The core gameplay is just about fun for a few hours. But if you want to play a great action RPG, play the original Diablo II or try Titan Quest from Iron Lore, which is a much better game.