A very trash and amazing game.
Right under the mess this game is loaded with is a really fun FPS, but it takes such an extremely long time to actually get to the actual enjoyable parts about it—almost a whole playthrough's worth or more—that it's very easy to just stop playing the game before even finishing it.

The tutorials the game try to show you are terrible. They'll show you videos of how to do certain functions, but don't actually teach you much, so it's up to you to figure out the game's mechanics on your own. It really doesn't help much that the game is full of little RPG stat details you're expected to learn as well on top of the game's many functions.

The story of the game is extremely surreal and interesting, however due to that surrealism combined with the poor English translation, it can be very hard to follow along as well to the point you'll probably have to read up on other people's analysis of the story to get it, even though the actual game's story isn't very long. Its story is so odd that when important NPC's die seemingly by accident and then come back in the next chapter as if nothing happened, I couldn't tell if they were just developer oversights—since the game's so full of jank—or if it was part of the game's bizarre theme.

The maps can be pretty atmospheric, but are way too huge in this game, so running around objective to objective can be a big chore as a result with nothing in between. If you try to run around and explore these big maps on your own, you're most likely going to be punished by finding absolutely nothing in the end—not even something pretty to look at.

Enemies in this game can be a real pain.
They respawn in waves at specific locations when the camera isn't turned toward said locations. You can turn down the spawn rate and even the difficulty itself at any time to at least mitigate this somewhat. The AI in this game are just Source engine multiplayer bots and whatever else Half-Life 2 may have regarding AI, so there won't be anything clever about them, making the AI both easily exploitable and very tough to deal with.
In the first real level of the game, the frustration can start right away as enemies can spot you from way too far a distance seemingly endlessly on the default setting, and this kind of thing only gets worse as you keep progressing where the type of enemies get stronger.

If you can somehow look past the broken mess this game throws at you as well as learning first-hand how to deal with the general jank & difficulty, you MIGHT finally start enjoying the ridiculousness of its actual gameplay.
It tries to be an RPG that encourages various character builds, but the game is awful to play on a new character as you're just too slow and too underpowered at the start, so it's easier to just keep working on the one character.
When you manage to rack up plenty of skill points to put into stats and get enough money for more weapon & skill options, the game can get extremely fun. The FPS aspect of the game was already nice at the start with weapons feeling like they've got some serious kick to them, but combined with the arsenal of silly and practical skills you acquire later, you start enjoying the exploitable aspects, like being an immortal minigun-spraying tank constantly eating enemies' guns & ammo to replenish health and hurting yourself to replenish your energy so you can keep your shield skill lasting longer to be tanking everything, or being able to jump so high you don't even bother with the slow ladder-climbing most of the time anymore—you can even crush enemies by jumping on them. By that point, you'll actually want to turn up the difficulty and spawn rate for the game to be more fair. Your character's also a lot faster and conserves more energy when sprinting, so the big maps aren't much of an issue either combined with you already being familiar with said big maps—even better if you get the teleporting skill that lets you instantly teleport inside enemies and killing them, essentially telefragging them, no matter the distance so long as they're visible and you're aimed at them.

It's a very hard game to get into, especially since it takes so much effort & time to get to the parts that makes the game so fun.