+++Edit: Please try see my post about Arch Warhammer without being biased about what he said in some of his videos. I dont necesarily agree on what he said about the DoW Games in general. I watched some of his videos about the lore and also read a lot of stories out of 40k codexes, rule books and the white dwarf back in the day.+++
He talks very precisely about the lore of races, special units such as Terminators (and why its impossible to jump in a suit of tactical dreadnought armor [nope, not even a primarch can do it]) and race traits like the exceptional tactical abilities of the Tyranids to perfectly time sychronized attacks of the their specialist units on enemy battlelines.
The videos have mostly a length between 30 and 60 minutes and are very good in expressing all the details of the lore.
Id just check if he has a video about something you are thinking of actually implemeting in the game to make it feel more like 40k. It would only help making this great game even better. The videos are not long and entertaining if youre somewhat in the 40k universe. Just give it a try!