all games are not created equal

I already compared OoTW with another game earlier, which sparked me to finally check out another game from the same producer, Eric Chahi.

Quick recap, OoTW was a very cinematic sidescroller that had engaging cinematics, no spoken dialogue (with the exception of a couple lines spoken from the aliens that you can't understand), and a great variety of level design and gameplay.

I finally checked out Heart of Darkness, and was quite amused!  It honestly felt like playing a version of Out of This World that I never seen before.  HoD does contain traditional cinematics to fill in the story, complete with English dialogue.
I skipped most of the beginning cutscene, though I understand enough that you play as a young boy with a vast imagination.  He wears a colendar as a helmet, and somehow starts with a lightning gun.  He can use this gun to zap the main villains, which are these little shadow demons. 
It plays much like OoTW in that every screen feels like it's own puzzle, where you have to think and plan how you want to tackle the obstacles.  For example, one of the first screens has you blocked by a large shadow being.  The shadow is create by some suspended stationary bones.  You use your lightning gun to destroy the bones and the shadow monster is gone. 

While HoD is certainly more bright and colorful, and the characters are pretty loveable, I can't say it beats the original.  HoD feels a little twisted, almost like American McGee's Alice.  OoTW is genuinely very dark and gritty, however.  The lack of any dialogue in OoTW is also preferable. 

Both of these games had a huge impact on me as a youngling.  They were very cinematic, very engaging, and offered many ways to watch your character die. 

Out of This World (the American title of the same game, Another World) is technically a sidescroller action game, but it plays very differently from most anything you have probably played before.  The game follows the story of young-genius Lester as he gets zapped during some sort of generic science expirement (particle acceleration, yadda yadda yadda).  The game opens with a fairly long cinematic, for early-mid 90's standards.  Once you watch Lester get zapped OUT OF THIS WORLD (dun dun duuunnnnn), you are then thrown in control of Lester as he starts to drown.  Then you will die, because you didn't realize that you're actually controlling the game at this point and Lester will get sucked into the deep abyss by some tentacle monster.
You will die in this game.  A LOT.  Anything that even remotely looks dangerous, is.  You have ONE companion in the entire game, and he will save your live more times than you can think.  Everyone else, however, will murder you over and over and over. 
The game is comprised of puzzles, in a way.  sometimes you just need to have a firefight, other times you need to think of sneaky ways to eliminate your enemies (one particularly entertaining instance has you kicking a guy in the crotch).  However, once you know how exactly to tackle all the obstacles, you can literally beat this entire game in 30 minutes.  Figuring it all out the first time, however, is extremely rewarding.

Flashback: Quest for Identity sort of combines Blade Runner and Out of This World.  The universe is under threat of an alien menace who are hiding in plain sight by disguising themselves as humans.  You start the game watching Conrad escape from alien captivity after suffering amnesia.  You wake up after crashing and the game begins. 
Flashback follows a more traditional style of gameplay.  You can run, jump, climb up on ledges, take elevators, shoot, and duck n' roll.
Like Out of This World, you can also die a lot.  You'll fight mutants, crooked cops, tiny robots, cyborgs, and morphing aliens.

Flashback is a lot more combat oriented than OoTW is.  However, Flashback will also give you much more gameplay.  Also, Flashback has always been critically praise for it's very smooth animation and intriguing cutscenes (particularly during the scene where Conrad gets his memory back).  OoTW looks good too, but the framerate gets incredibly choppy and is usually all over the place, depending on how much is happening on the screen.
Many elements of modern platformers have taken elements from these games, especially Flashback.  One particular noteworth example is Oddworld: Abe's Odysee and Oddworld: Abe's Exodus.  Play Flashback and one of these games back to back and you will definitely find some similarities in the controls.

I love both these games and have played them through many many times before.  I highly recommend them both if you haven't played either one.  Flashback wins for length, graphics, and gameplay.