I don't think it's a AMAZING game, but it's fun and chill. There's a bunch of little things that bug me - the big headed character models, the lack of any kind of ceiling in first person mode, the lack of customization with regards to themes or aesthetics, that king of thing - but the major things are all good. A bit simpler than something like Roller Coaster Tycoon or Theme Hospital, but still a lot of fun in the same vein. Manage your aquarium, set up your fish tanks so that they don't eat each other, hire enough staff to feed everyone, and you're golden. It's pretty easy to get the basic feel for how to run things and from there, it's just a laid back management sim with some fish. Game runs well, interface is fine, no technical issues. It's probably not going to be your game of the year, but it's a fun experience and I'd efinitely say it's worth what it costs.
The tagline for this game is that it's a "reverse horror game" where you play the monster, but aside from killing some unarmed civillians, it doesn't really do much with the horror aspect. It's mostly just a kind of short, linear metroidvania game. To be clear, it's not BAD, the atmosphere create with the sound and graphics is good, but the gameplay is problematic. Your abilities are tied to your size, which is tied to your health. This means that to solve certain puzzles you need to be a certain size, which means a lot of backtracking to the points in the map where you can grow or shrink. Controls are imprecise (especially late in the game when you get fairly large) so combat tends to be extremely simple and clumsy. There's not really much of a story or characters or anything like that, to carry the "horror" side of it, either. Again, it's not the worst, and for the four or five hours it lasts it's decent enough, but maybe wait for a sale if you're not sure.
I generally disable this DLC in my games, I really do not find it fun. The DLC is cheap (the only reason I didn't give it one star) but only adds one neutral monster: the Lord of Skulls. The Lord will show up at random, allegedly near the current strongest player, rampage around the world killing everything around him for ten turns, and then vanish for a while. Then he'll come back again and start over. Killing the Lord gives you a boost to your defense. The unit is ridiculously strong, powerful enough to take on entire armies, and raze a city to the ground in just a few turns if your army is too far away to get there in time. Basically a middle finger to new players, and a kind of a "victory tax" for veterans. Depending on where it decides to spawn in and how it decides to move after that, it can neuter an entire faction, which is just too much power for a random element to swing for my taste. Either way, not really my idea of fun.
tl; dr: It's very derivatve of Halo, but dodgy controls and terrible sound design drag it down and there's not much aside from the 40K setting that would cause me to recommend it. So, to start, I can't really run the game. Clicking "play" in the Gog launcher just throws an error message. The EXE runs on it's own without the launcher, but I can't run the config utility either, so it's possible that your mileage may vary. As someone who really likes 40K, Fire Warrior always had a kind of mythical status to me, since it was the only 40K FPS for a long time, and you couldn't buy it anywhere. So, I was super excited to see it on Gog. Unfortunately, most of the game is just decent, not really "good," and doesn't even reach that level in some aspects. For example, the sound design is terrible. Everything that's not a solid tone has been bitcrushed to a massive degree so that the whole game sounds muffled. There's no music, either, and volume mixing is awful when characters are talking. The other major problem is that this game has the floaty controls of an early console port. It's one of the only FPS I would ever suggest to play with autoaim on, because moving the mouse is so weird feeling. It's aggrivated by the fact that the weapons in this game are inaccurate as heck. This is not really a huge problem at the beginning of the game, since your weapons are mostly machine guns or shotguns where accuracy is not a major issue, but later on, when you get slow firing weapons like bolters, and are fighting enemies with massive health totals, it gets really frustrating. Aiming at center of mass at an enemy maybe ten feet away, pulling the trigger, and watching the shot whiff half the time is not fun, and the end game is basically that experience for three or four hours. So many fights ended up just feeling like dice rolls because of this. So, yeah. Not terrible, but not great, and enough "not fun" problems that I can't really recommend it.