I'll revive this thread again, to say that I'm in the closed beta, and it is a fairly decent game so far.
The hack&slash part is classic Diablo-like. The action is fast-paced and good fun, most dungeon runs are shorter than 3 mins. I can play it for about an hour at a time before it gets a bit boring.
The "build your own castle" part is somewhat reminiscent of those browser based games (Ogame, Travian, and all their siblings), in that you get to upgrade a handful of buildings with exponentially increasing costs and build times, the 2 resources being gold and life essence (blue crystal). You even build small upgradeable mines in your dungeon to have some passive income. The one thing that differs is how detailed the defense management is. You get to build your dungeon from basic rooms - there's a large choice - and put monsters and traps in it, although there are many limitations on how close and how many they can be.
The most fun for me was when recently (2 days in) many players started storming my castle. I got to watch their replays and seeing them die is always satisfying, while seeing how they beat my challenge gives me ideas to improve my design and maybe even some tricks to beat other people's dungeons.
All in all the game feels very polished even in closed beta, it feels like a finished product already. The design is cartoony but it perfectly fits with the atmosphere.
The only thing I really dislike is the cash shop, you need to pay real money to reduce building times (remember, they increase exponentially). Also, at first you can build/upgrade only 1 thing at a time and you can get the upgrade to build two things easily with the little amount of cash shop currency they throw at you in the early quests, but more than that and you have to pay from your own pocket. I do understand that they need to get paid from their work but I'd love it if it didn't interfere with the gameplay (League of Legends does it very well in my opinion).