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

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.