Okay - Honestly.  Its much better now than what it was on release.  It has a strong single player campaign and many multiplayer options.  It is a bit of a grind fest, but them most ARPGs are, the grind is where a lot of the game is same-y, mainly because of using the same maps.  Weirdly though the campaign uses some of its own maps which are stunning, the hive city springs to mind.

Working knowledge of the 40k universe and lore is very handy, otherwise you'll need to do a lot of reading.  If you're a fan - your laughing - the graphics, gameplay and story are very grim-dark 40k - and this is where Neocore nailed it. 

Builds - well - from what I have played so far, they are diverse in their own class only.  I'm really not sure you could turn an Assassin into a heavy crusader for example. You can experiment inside your own class quite a bit though.  An example of this would be my ranged crusader, he has a 2 handed storm hammer as his secondary weapon - and if I invest enough points into melee he would be good at both - ect.

A lot of these issues have improved with the last update (3-7-18) and the campaign is even bigger, there are a lot bugs but Neocore are fixing them - so I can't fault them there.  

Overall I recommend you go for it - it can only get better, and if you need a friend for co-op give me a shout - I'll be happy to help you out. (let me know here if you do!).

Don't forget though - this my opinion only! ;)

Reviews on steam page can help to understand what is the game all about and how its doing right now