Vampire The Masquerade: Bloodlines is a beloved game with a cult following. It's an amazing game that is extremely unique. I'd like very much to see it here on GOG, but even if it never comes here, go buy the darn game anyway, it's worth the $20 it usually is when not on sale.
The Positives:
Your choice of clan matters: There are seven playable clans (types of vampire) with others making an appearance. Beyond the expected uniqueness of each clan's abilities, each clan has some degree of unique dialogue just based on their clan alone. For three of the clans, much of the entire game's dialogue was re-written/adjusted just for them.
NPCs' actions and words are at least partly based on your clan, a Ventrue is likely to respond more positively to a fellow Ventrue as opposed to a Brujah. This system even affects rewards at times.
Quest Flexibility: Most of the quests can be solved in a couple of different ways. Stealth is a legitimate playstyle, so is action of course and in many cases you can just talk your way to wherever/whatever you need. The flexibility doesn't just revolve around plastyles, you can also choose to double cross people...fairly often.
Choice and Consequence: This is perhaps this games bread and butter. There are many times you're put in situations where you have to make a choice and live with it's consequences. Some of the situations are small, some are important. For example: An old friend recognizes you and is shocked and thrilled that you're alive, do you convince them that they're mistaken and in doing so keep the secret of vampires just that, or do you cheerfully greet them and risk breaking the masquerade. Many of the situations are rather low key and in the grand scheme of things, unimportant, but there are more than a few times you'll be faced with some big decisions.
General story/dialogue/setting/atmosphere/general design: This game is extremely well written, both for the story itself and the dialogue. I would go so far as to say the dialogue alone is worth it's price. It's atmosphere and it's relation to it's setting is amazing, each area has it's own feel, but it all feels connected. You actually have to explore and talk to seemingly random people to get certain sidequests, and there is at least one quest giving NPC you'll never meet if you don't explore something seemingly out of the way and unimportant.
The Negatives:
Bugs/Glitches: Fanmade patches have fixed most of the bugs/glitches that are fixable..but it remains buggy/glitchy. Now it's not exactly full of game ending bugs/glitches (though there are still one or two) but some people just have problems getting it to run. Personally I often have to start the game, close it using Task Manager and then restart in order to get it to run. However most of the bugs/glitches are pretty benign, like a graphics glitch where power lines freak out and act like somebody is playing jump rope with them.
The end sequence (the last couple of missions): For most of the game you have a large degree of freedom in how you can choose to complete quests, in the end sequence you are railroaded into a couple of action only levels. Spent all of your experience points making your character into a stealthy fast talking vampire version of a used car salesman who can't fight their way out of a wet paper bag? Enjoy your mandatory boss fights. No, the game doesn't scale it's bosses down to suit your build. So yeah...enjoy.
Oh...and the sewer level. I guarantee that halfway through the sewer level your thought process will be around the lines of "is it over yet...nope. is it over yet...nope. is it over yet...MAYBE OH MY GOSH...wait...nope"