...don't know what world you live in, but if anything, 40K has become LESS ridiculous and over the top and much more mature recently, largely due to contributions of people like Aaron Dembski Bowden, McNeil, and Abnett (may the Emperor Bless Them Thrice).While all you say this true this was more true of 40k a little while ago it's become less and less of that setting as GW finds new and inventive ways to ruin the good thing that they have, it's become less and less interesting.
Over the past few years Space Marines have become more than emotion-less supermen, the primarchs were given actual substance, and there is actual lots of historical context to make the crazy stuff we see in universe make a lot more sense.
Unless you are talking about the arch-idiot of 40K, Matt Ward (May the Emperor, peace be upon His name, destroy him a thousand times over), then 40K lore has improved rather consistently to being more grown up.
The point is NOT to get invested in the good guys. It's to get invested in whoever you want. You can just easily get invested in Chaos as you can in the Imperium of man. Especially since the HH has started publishing. That's a good thing.Everything is so grim and there is no hope of things getting better there is no point in get invested in the "good guys" struggle as you know they'll lose (for reference the "good guys" in 40k are the Immperium of Man, Craftworld Eldar, and the Tau). Plus as I said GW is running the setting into the ground.
Also, it's hard to call the Imperium or the Eldar, people perfectly happy and, in fact, planning on, complete genocide, as the good guys. The Tau are slightly better, but not by all that much.
It's also probably the biggest modern scifi franchise outside of Star Wars and Star Trek, so its' hardly surprising one of the most popular extent scifi universe around has lots of people talking about a sci-fi game.All that said 40k fans might want to tame their enthusiasm a bit the vibe I'm getting from the game is clearly more Star Trek/Mass Effect type of thing then its 40k. Honestly I'm surprised that 40k has had the presence it has on this sub forum. Then again 40k is a wargameing franchise so maybe I shouldn't be surprised.