Okay, so there are a couple things missing that would have made it an instant buy. 1. It's missing character customization, which while not necessary, would have been a big draw. 2. It's missing a good narative. They could have made the campaign feel more continuous by having some cutscenes or something, but instead the game feels very 'instanced', and you kinda have to figure out the story through the mission briefings/missions themselves.
Now, aside from those things I think this is a good, smart game. It feels like the movie Aliens meets WH40K- you root for some of the biggest badasses in the universe to mulch some xeno filth and get out alive, but of course the aliens are smart, agile, and extremely deadly if they get close to the humies. So, the game retains the feeling of dread at finding out exactly how many genestealers are around the corner, and how likely you are to be pressed for AP/CP (the action points you use to command your units to do anything). The game is difficult, but never seems outright unfair. The Terminators and Genestealers feel suprisingly balanced considering one's ranged profficiency, and one's melee profficiency. Providing the map isn't nothing but corridors, the genestealers have plenty of chances to get the drop on you and eliminate your troops one by one. Genestealers actually have some interesting abilities. While their units don't have special attacks, or really any variation (except for the broodlords), they can choose to either be stealthy, or to play the waiting game and build up forces, or to just rush the Terminators every turn so they can't continue through the mission, and pray units get through to cut them in half. This is because the Genestealer player (or AI) can choose to put units at any number of spawn points, can choose whether or not to reveal units at certain times, and can make big moves each turn due to having more AP.
Overall, I feel like the game is a good buy. The Terminators are weighty and have heavy firepower, which looks and sounds great. The Genestealers are appropriately creepy, but could probably have benefitted from some better move animations and dodge animations, but otherwise look like a fearsome foe. The game knows it's theme and keeps to it. Even though the game deals with a lot of hallways which could have been a lot more boring, they find ways to keep them interesting (flickering lights, gore, weird tech, ominous mists and steams, all the usual wrought metal and skulls you love from the Imperium, etc.). The gameplay is fun, with different objectives on each map for the Terminators (rescue, destruction, retrieval, escape, etc.) and so it stays fresh through the campaign.
Finally, the shoulder cam is awesome, the emperor protects, and I rate this game an 7/10.