Let me start by saying I never played the original game. I know, quite a shame, but this 20th anniversary version is the perfect chance to try it out. Be warned, though, despite colorful and beautiful new scenarios and slight graphic remake, this is still a 90's game. Which means that it remains a true game in spirit, not to be confused with the nursery school games they make these days. It is quite difficult, and you may not be able to complete it without serious commitment.
The game can be finished in under 20 minutes once you master it, but don't be surprised if it takes you several hours just to see the next section. It appeared to me that there are at least a couple of sections in the game which need previous knowledge on how to solve them. Therein lies the biggest flaw of the game: I really don't think you can finish it without knowing precisely what to do in some parts, and you'll definitely say "that is SO random". Yes, you will die a lot, and hopefully each death will give you extra info on what to do next, but the game feels sometimes cheap and based on trial-and-error. Perhaps too much.
This is not a serious flaw, though. You can always watch a walkthrough of a certain part you're stuck with and realize you missed the most random thing, such as shooting a chandelier or letting a guy bomb the floor below before you kill it. Either way, this will not take away the general immersion and feeling of awesomeness from the game. Even today, it sucked me into that other world and getting to care about Lester and his buddy. Once you discover the way to proceed in what seemed like an impossible situation, it feels very rewarding. This is coming from a guy who hated Dark Souls because it was too punishing and not rewarding.
I would've given this game a 9 because you can truly see how it changed gaming in the 90's and became an instant classic, but due to its nigh-impossible situations that will test you to the limit, I'll give it an 8 because it's a bit hardcore. If you can manage it, though, it'll be one of the greatest adventures you have ever played. It'll stick in your mind and hold a very, very high score in your game memory records. Give it a try!