Taste of demo made me excited for this. I though I'd finally get a new game that is similar to Heroes of Might & Magic except with choice system, romanceable companions, visible gear/armour changes, etc.
Instead it just feels empty and shallow, introduction to the world almost does not exist which leads to Player pretty much not caring about any of the characters.
Artificial barriers of "you must progress further in the story" make the early game rather boring. You can see what Units will available in the future yet you are left "spamming" the same ones for quite a bit of time.

Devs: "Let's make a horror game whose setting is in Hell. We'll call it Agony."
Post-Agony release
Devs: "Darn, Agony didn't work. Let's now make DOOM-like except with tits and repetitive content. And let's call it in the name of sex demons and give Protagonist the most annoying voice. Who cares if we only learned a bit from our past mistakes. It will work, right?"

Very beautiful and cute... but the gameplay's kind of too lackluster to bother finishing it.

Simon says it's artsy.
Simon says its platforming is boring.
Simon says drugs, drugs for everyone!

I really liked it until I finished Von Braun and had to go "searching for X amount of things" in confusing no-map place, where things got tedious and kinda annoying. There were some great parts after that but it just didn't feel the same anymore.
I should preface that because I didn't fully understand how the early choices work I ended up a Psi/Melee char. Yet melee hitboxes quite often didn't work properly and some of psi skills were kinda...useless, making the experience less and less enjoyable as more enemies were introduced into the respawn system.
I heard there will be Remake of 1 and Remaster/Enchanced version of this so I might give these a try.

Frankly, it is too long. Felt burnt out at the end of main story and didn't even get to the DLCs because, well, after "farming" some gear my save literally disappeared.

Played with GMDX mod (was advised to use that instead of Revision for 1st playthrough).
Has some great parts, but also has parts where it's reaaally far from being called "perfect" or "masterpiece".
Nonlethal and/or Stealth runs are possible but can become tedious & boring. I abandoned going nonlethal-stealth after certain mission, seeing that there's not much variety in nonlethal take-downs when compared to lethal.
Stealth also can be annoying. Better keep your inventory organized or you won't be able to pick up a body (imagine that). Also had occasions where enemies saw me almost through walls or when they technically should only be able to see a tiny part of the body. There's more I'd want to complain in that regard, but I'll keep this spoiler-free.
Story is okay, world-building seemed bit lackluster, only cared about one or two characters besides MC.
tl;dr Enjoyable but rough around the edges even with "massive" mod overhauls around.