I disagree with the previous poster, I DO think this is WH40K Diablo.  When my friends have asked me about this I ask "Do you like Diablo?" and "Do you like WH40K?"  If the answer to these questions is yes, then this game is a must buy.

There are definitely some differences though:

1) Gear - Diablo has much more varied gear and gear sets.  The gear sets look unique and much of the leveling gear does dive you a different look as you progress.  WH-I does not.  While the gear does create a few different looks, they are not quite as varied.  No gear sets.

2) environments - Diablo randomly generates the maps and those maps have more elements and are more varied.  They are bigger as well.  The environments in WH-I feel fairly static and enclosed.

3) music/sound - the music in diablo is fantastic and the ambient sound is great.  The music and sound in WH-I is good but now on the same level as diablo.  Voice acting in both games is very good.

4) I haven't played co-op in WH-I but now that they have added it to the game, I'm guessing it adds a lot to the gameplay.

5) diablo has a bunch of little secrets/Easter eggs/fun additional stuff.  WH-I does not.

But I still go back to the basic criteria, if you like Diablo and WH40K, you will like this game.

To be blunt you have to answer these few questions? Do you know and enjoy the lore of the Inquisition in the Warhammer 40K setting? Do you enjoy a top downn Action RPG? IT IS NOT DIABLO WH40K! If you can honestly answer yes to those questions posed I would say WAIT til base game Warhammer 40,000: Inquisitor- Martyr  is on sale again and buy it first since it has an OK story that leads into Prophecy

 If you really want to play as the Tech-Adept you wont get the initial story line. BE WARNED unlike the PC which is a stand alone expansion YOU WILL NEED WH40K INQUISITOR MARTYR TO PLAY PROPHECY.If you want to add me as an Xbox freind message me a short 'Neocore forum' at BEKKA TORAVU and I can elaborate more