Outdated and insufferable, even by the standards of the 2000's it's not good.
I wouldn't say it's a stealth game, i never even needed to hit the crouch button, it's more like an FPS with some stealth elements, and point & click-esque puzzle solving.

You have to find the solutions to each step in the mission by trial and error, there's no in-level saves and enemies stay aggro even after you respawn, so to complete each mission you'll have to retry it several times;
Some of the maps are way bigger than they have any right being, and place you on the other side of the objective so every time you do restart you have to walk across it for minutes before even getting another shot at it. (Special shout out to the Colombia levels, specially the last one where it spawns you on a spot exactly opposite to the only gate into the compound and you have to go around the whole thing, honorable mention to the last Rotterdam level where you have to wait for all the guard patrols to go around the docks to the boat)

Sometimes it does a good job at hinting what you should do next (like with the bartender in the Lee Hong Assassination or the trail of conversations that leads you to Fritz Fuchs in Traditions of the Trade), sometimes it expects you to somehow figure out things on your own that make no sense (like hoping across balconies in Traditions of the Trade; something you only ever do in that one spot and once in the tutorial, or having to shadow the guards to go through the gates in Plutonium runs loose).

The combat is terrible, with wildly inaccurate guns and way lower damage to bodies compared to heads, even though it's required for some of the levels (I don't even know how you're supposed to clear the last level without cheesing it)

That being said, i had little bits of fun now and then, Sneakily killing the guards around one by one was fun; and you get the tiniest glimpse of the vibe the developers would achieve later in the series.

I've made myself play through it in order to play all of the Hitman franchise, but i would recommend skipping this one, I've heard Contracts remakes the best levels and retells the story in this one anyway.

Awesome game, it's about hit man, hit man dont get hit man you will die man

This a good game. Very fun, when everthing goes as planned. Although if you are a new hitman player coming into this game after playing the WoA Trilogy, you will find its nothing like the newer games. You have only a few ways to do your objective. And sometimes its confusing on what youre supposed to do. Honestly i dont blame you if you open up the console and cheat, because some levels are brutal. And with no saving its hard to finish some levels without tearing your hair out. Although i highly reccomend you try this game, its interesting to see where the series started.