Tl;dwr - Astartes is short, to the point, and pretty much perfect.
A fan creation in an established franchise getting notice and praise from the people officially in charge of that franchise is fairly rare. A fan creation in a franchise that is good enough to draw people into the fanbase due to its quality is even rarer. A fan creation that does both of these things, AND gets the people that officially run the franchise to outright hire the creator(s) is something else entirely. As you may or may not know, Syama Pedersen, the man who created Astartes, was hired by GW to work on other projects for them. The last time I remember that happening was with Alexander Velicky, a modder for Skyrim who created the Falskaar mod. Bungie was so impressed with his work that they hired him. That was back in 2013. That should tell you everything you need to know about Astartes.
A fan creation in an established franchise getting notice and praise from the people officially in charge of that franchise is fairly rare. A fan creation in a franchise that is good enough to draw people into the fanbase due to its quality is even rarer. A fan creation that does both of these things, AND gets the people that officially run the franchise to outright hire the creator(s) is something else entirely. As you may or may not know, Syama Pedersen, the man who created Astartes, was hired by GW to work on other projects for them. The last time I remember that happening was with Alexander Velicky, a modder for Skyrim who created the Falskaar mod. Bungie was so impressed with his work that they hired him. That was back in 2013. That should tell you everything you need to know about Astartes.