I actually replayed for the billionth time TDP two or three months ago and it's as good as ever, what an unbelievably fucking great game it is. Sure the graphics and animations may have aged but the visual (not the technical aspect but how the game actually looks like) is just amazing, it shits over everything else. Almost 20 years later it still lectures any other game in atmosphere. Sound wise, not only it didn't aged at all, it's still miles ahead of pretty much anything.
I could talk reasons why that game is amazing for ages. I love the rhythm of the story, I like how the main arch is the Trickster "quest" but you don't start the game with Victoria looking for Garrett, you start much earlier and get to see some of his operations and adventures before getting involved in that. Just think about that for a second, it may sound like a small detail but it certainly isn't, I can literally bet my ass that no such thing would be made today, a game with that story would start at Victoria and Constantine and scrap all the previous stuff. It'd probably tell you about Garrett's previous stuff through "audiologs"
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It's brilliant. The first three missions serve as a small trilogy that has its own arch and introduces you to the creepy, supernatural side of that universe. It shows you how dangerous and full of crazy shit hiding in the depths and darkness that world is. Bafford Manor shows you how's Garrett's "usual" kind of job. The scepter's dealer got caught by the Hammerites and you go free him to receive payment for that. This is when the game gets you by the balls and go full "SURPRISE BITCH, THIS WORLD HAS UNDEADS" but it isn't some random stupidity, it's a creepy abandoned mine that you went in as an alternate way inside the prison. Then way above you even see a mage throwing spells, but there's only one guy in the whole level that does that and he's clearly a superior priest of sorts, in front of an altar. Again, what game today would take the proper care with stuff like this instead of filling the Hammer's barracks with dozens of spellcasters of all kinds? Anyway, guy dies, you won't receive your gold from him, but you happen to discover some interesting stuff about this mystical horn way down in a crypt. The game cleverly presented you the haunted side of that world and now it's inviting you to go down a crypt, when that level starts you already know shit will get serious.
Bonehoard is just beyond stellar, it's possibly the best dungeon ever made in any game including RPGs. It has everything, all kinds of traps, all kinds of creepy stuff, monsters, undeads, and it's so masterfully put together. When you finish climbing those stairs and look for the first time at the horn, the feeling of pure satisfaction and reward is so great.
Now you're a rich Thief, time to upgrade your arsenal with the newest lockpicks in town! Only someone shoots an arrow at your dealer's head thinkng that was you. This is when the game properly presents you the City (while you chase the assassins) and again a castle breaking situation to scratch that newly acquired itch that you now have after Bafford. In this mission, LGS again shows you the dirty side of those people using only the environment (Ramirez has secret corridors behind the walls with small holes to peek through and watch guests rooms; in the Hammerite prison you could find alcohol hidden at the priest's bedroom), I don't think I need to say how that's another kind of subtlety we don't see in games anymore. Also, Garrett's initial plan was to get the lockpicks and go steal a Hammerite temple in the City. Even if that objective is immediately cancelled, it's great to have it because it shows that the situation got out of control and you now have new problems to deal with. The series play with that many other times and I always liked it. It's like small, contextual plot twists that makes a level go very unpredictable ways. Like Song of the Caverns, that you'd think it'll be a monster level only for you go up and into an Opera house.
And ONLY after all this (and Thieves Guild) the actual story of the game starts. I mean, four of the most entertaining missions ever were just an introduction. Some games would die to have a Bonehoard serving as its high moment. TDP has it as a preface.