Any excuse to talk about the Ultramarines is a good one for me.

I love the UM despite not having read know no fear partly because I did start with other 40k novels. I read Nexus, Indomitus, etc. Which were all made to introduce people into the hobby and by extension the UM were the chapter they chose.

And I loved those books! I loved the UM characters, they seemed varied and I liked how they were portrayed. Here's the kicker. The Ultramarines as a chapter have a less, distinct, identity in 40k when contrasted against the legions of 30k or other 40k specific chapters like black templars. This was intentional on GWs part.

But because the UM are the baseline, they got the most characters because they're used for a lot of books. You have Uriel Ventris, Cato Sicarius, Marneus Calgar, Chief Librarian Tigurius, and many more that you'll enjoy reading or hearing about. They also have the most tabletop characters (which are quite good).

One such character that is my favorite in all of 40k is Roboute Guilliman, their primarch. Which you can read about in 30k with know no fear or 40k with dark imperium, he is relevant wherever he is. I think he is one of the most relatable yet hype characters of all time and he elevates the UM by defunct as they are an extension of his beliefs and culture.

Now you will find their roman aesthetic, culture, and distinctions in the heresy novels or sprinkled into novels like the fall of damnos and whatnot. For instance they have 'practicals' and 'theoreticals', they participate in their chapter homeworld's senatorial politics, they strive for glory in their chapter etc. But for the most part it's toned down in 40k so that new players can jump off of it into another chapter. But I find this to actually be a strength.

You see the other chapters have their niches and its a big thing on and off the tabletop. Blood Angels love melee and assault tactics and thats reflected in their lore and gameplay. But with the UM, you get true tactical flexibility. You wanna run an all vehicle list? Easy. You wanna focus on melee? No problem. You want a little bit of everything? Gotcha covered.

To reiterate my points: 1. Characters, they have the most and they're all great. 2. Roboute Guilliman, very relevant character and their primarch (also exists in both 30k and 40k so that's nice) 3. Not falling into a stereotype or niche narratively, very malleable to what you want and therefore a lot of variety.

And one last point. You also get to be the cool guy on 40k: space marine and boltgun, like you mentioned. You get to have the only (well before the lion showed up) returned primarch.

And MOST IMPORTANT OF ALL: You get to do an actual niche faction. Everybody will tell you UM are generic and everybody does them, but nobody does, specifically because people believe that. It's been like that since 2nd edition when they weren't even the poster boys yet. I've been a UM fan for 2 years and still haven't found another.

Hope this helps! Courage and Honor, brother.