What would you recommend if I was more interested in Tyranid lore & fluff? Any good reads in that regard?
Theres few with the Tyranids as the protagonist/main character. They usually show up as the big bad (either in a grand/splinter invasion or through subtler means via the Genestealer Cults). They show up every now and then in the Cain novels. "Warriors of Ultramar" (2nd book in Ultramarines series) is suppose to be a great one detailing a Tyranid invasion. A lot of people are lauding "Devestation of Baal" (Nids vs Blood Angels) for Tyranid lore too.
Other than the Cain books I have only read a few short stores like "The Fall of Malvolion" which was a good depiction of how dire a full on hive fleet invasion can be to the unsuspecting. There was also a short story by the King of Space Wolves novels (William King) "In the Belly of the Beast" about a space wolf scouting mission on a mysterious ship found that seems to be organic. I read both short stories in the anthology book "Let the Galaxy Burn" which has great short stories that flesh out the whole universe. It was published in the mid 2000s so it may be hard to get a physical copy but I am sure you can probably find them on the interwebs.
As for Genestealer Cults (GSC) there is the novel Cult of the Spiral Dawn. I also like this fan made video from the TTS guys for Halloween a few years back. Its a lovecraftian telling (and homage to the xbox game "Call of Cthulhu") of a GSC set in the universe of "If the Emperor Had a Text To Speech Device" (often referred to as TTS).
https://www.youtube.com/watch?v=Ep_1k-lOto8If you like webcomics "Servants of the Imperium" is a comedy 40k webcomic about an Inquisitor and his crew that run into a few misadventures (its based on the Inquisition table top RPG game) and has an "Order of the Stick" style artwork. The comic starts in Black and White and after a handful of strips its full color. They have a really fun and interesting GSC arc near the middle of the series that I re-read from time to time. I am glad you made me re-find the webcomic because it ended abruptly with a montage comic detailing what would of happened if he had time to finish it (this was a long time ago), but it looks like he finished it as I am seeing new comic panels than I remember and no longer that montage one.
The GSC arc starts around strip #63
https://www.servantsoftheimperium.com/index.phpEdit: Also if you're into video games Dawn of War 2 has you play as a Space Marine chapter (Blood Ravens) as their recruitment worlds are being invaded by a hive fleet. The story and action is really good. It plays like a squad based rpg strategy game. They also have this wonderful trailer:
https://www.youtube.com/watch?v=OTjyO_FncE4Its $20 on Steam:
https://store.steampowered.com/app/15620/Warhammer_40000_Dawn_of_War_II/There are sequels, one that continues the story of your team against a Chaos invasion, and a 3rd where the Inquisition shows up and you can play the campaign as any faction (the vanilla and first sequel games campaigns is only from the PoV of the Space Marines)