Alright,
as someone who played both the Duke's and Lion's version of the chapter master game (Duke's Interstellar army simulator 2015 as well) and hang out in a discord server of it, I guess I could give a review here...
So, chapter master. A simulator, where you control a group of genetically enhanced supersoldiers in a grim dark universe of warhammer 40,000.
The scope is basically - 1000 marines, plus leaders, and you managing their equipment, deployment and a few other things. There is a sector, which you potentially exist in and look after, with potentially making your existance less of a misery... So, perhaps relevant on a small scale, but insignificant on the grand scheme of things - there are no audiences with the Emperor, primarchs or even a possibility to flee to the star maelstorm.
You can't even take control of a planet right - despite Lion's improvements, the capability to get tithes from a planet requires you to visit it at least once, when loyal, only then you can consider installing a serf... And, Lion's improvement can be considered a downgrade when replacing your starting recruitment world's governor immediately, which forced me to scrap some renegade-playthrough strategies (Forge worlds are also a problem - installing a serf is simply not enough, to allow you to build ships and make the mechanicus shut up and not try to rebuild the Imperium's fleet)...
Still, save editing is probably the best addition to the game so far, with now giving you the option to experiment with it. Yet, there doesn't seem an easy way present to create Terra, or star Maelstorm...
I expected more! But okay. Maybe the large scale is simply too much for this small scale simulator. So what is missing?
The very lacking core feature, is the way of sector control takeover - there isn't really a way for you to instal an entire sector governor, or even proclaim yourself as one, effectively creating a petty imperium of your own. Renegade playthrough'ers have been somewhat disappointed (I probably should call myself Perturabo, for being such a fanboy, but it probably is already taken).
Another problem with narrative and feeling that the galaxy is alive - enemies and allies. The imperial guard exist as a separate entity, with which you hardly have any influence over (well, yes, you can battle out some 'heavy' presence tyranids, but there will be no indication that the guard are helping you activelly in combat in either way.) or any interaction with in general (there are only 3 types of allies (if loyal also) which you can recruit using diplomacy and then trade interaction. It's pretty sad that average guardsmen (and various combat vehicles) are not among them). And while we are on this - where are our serfs/slaves? I know that Dorn didn't care about them, but I want to have a way of testing the enemy's defences, in forms of expendable troops, and if you are trying to say that these 1000 sons are enough as expendable - sure, they are expendable - but I'd like to see how long are you going have their iron, with the enemies that you'll face in this galaxy. Recruiting Planetary Defence Forces would at least be acceptable compromise.
Speaking about diplomacy, it would be a great way, to make the Imperials (enemies, strangely, can already be defeated in combat. At least, some of them) with which you have diplomatic interactions with, replacable and actually existing on a planet. I'm sure at least 1 son of Leman Russ would approve, considering he beat up a nosy inquisitor once... So, making a planet or 2 have a "sector office", "inquisitor's office" and similar installations, which you can destroy or even clear out in a battle (perhaps your enemies could have this option too), resulting in the death of a character with which you've been (potentially) interacting, would definitely be a great addition.
Another common problem - acquisition of ships. Considering that it is a sector that you (try to) look after, no random junk floating in space will do. You need actual ships from mechanicum, obviously manipulating the stock market and selling you ships at a huge markup (ah yes, various games have an economy system in them, would be nice if it existed as well) with state of the art warp drives. Shame that you can't ally with the T'au, to get some slower, but nonetheless, a way, to move around. If lore is to be believed, ork ships may, sadly, be unusable...
Other nice features would be playing as other factions, but that can wait...
I suppose, we might need to change up some names here and there, with Geedubs being possesed, or maybe even depart from this WH40k, and create our own work of fiction...
Take the Iron within!