Chances are, if you’ve had an Internet connection at any point during the six years, you are familiar with Portal. Created by the Internet-beloved Valve and shipped with a set of games called The Orange Box back in 2007, Portal took the gaming world by storm.

Three years later, Valve released the eagerly awaited sequel, Portal 2, which expanded the gameplay and world of the original. Reviews were universally euphoric, and Valve had another hit on its hands.

Count me among Portal’s dedicated fans. I adore the original and love the sequel. What makes the game work? Let’s walk through it, point by point:

1. Great first-person puzzle gameplay

Obviously, Portal’s success starts with its ridiculously fun core mechanics. The game plays in first person, and you control a “portal gun” that doesn’t shoot bullets, but instead sticks portals on the walls. You stick a blue portal on one wall and an orange on the other, and you can travel through one portal to the other as if it’s an open doorway.

You start at Point A and have to use portals to get to Point B. It’s deceptively simple; that’s all there is too it. The fun comes in the game’s mind-bending puzzles and permutations on this simple portal gameplay.

“Now you’re thinking with portals!” was a marketing catch phrase for the series as Portal 2 prepared for launch, and it’s true: You have to wrap your head around the wacky physics involved with portals. Concepts like momentum and gravity all of the sudden do not behave the way that your brain intuitively expects them to.

Portal 1’s favorite trick is to force you to figure out how to increase your momentum and strategically place a portal so you shoot to the correct spot. Portal 2 expands its repertoire of puzzles a little bit more and introduces “slimes,” or new ways to alter the physics of surfaces.

It’s fun to just play around with the portals and see what craziness you can come up with, and the puzzles are the right amount of challenging to encourage you to keep experimenting. It’s a great system.

2. The characters and humor

All that said, Portal would have been a fraction as zeitgeisty as it was if not for its great, dark comedic personality. Your guide through the world of portals is a female computer voice called “GLaDOS,” a computer system owned by Aperture Science, whom you are a test subject for. The way she constantly berates you, jokes of the demise of humans, and twists corporate speak in dark ways is just as responsible for the charm of Portal as its gameplay.

One fan favorite joke: Because some tests supposedly require another person, GLaDOS gives you a “teammate,” a “weighted companion cube” or a box with a heart drawn on it supposed to represent your friend.

Another: GLaDOS promises you cake at the end of your testing, but — suffice it to say — there is no cake.

Portal 2 introduces some new characters, including the friendly AI Wheatley, Aperture Science founder Cave Johnson, a gun turret that has become sentient, and a “personality core” particularly obsessed with space.

The second game has some new favorite jokes. Johnson has a legendary rant about lemons, GLaDOS has a memorable encounter with a potato, the corrupted moon-obsessed core gets everything he always dreamed of, and the companion cube makes one last, perfect appearance.

The sequel doesn’t have quite the same impact as the original, in my opinion, simply because expectations were so high, but it’s still undeniably great.

3. The endings

Egads, these endings!

First, I would encourage you to jump ahead to point #4 if you haven’t played these games and are thinking of it, because I don’t want to spoil the fun twists for you.

So, Portal spends about 2/3 of its duration with you as a test subject completing an experiment. You are promised cake at the end of the trial, and you hop on a conveyer belt platform to go claim your reward. But when you round the corner, you see you’re headed for a fire.

Thinking quickly, you can shoot portals to escape the conveyor belt and escape through the dirty pipes and underground facilities of the Aperture Science building. GLaDOS tries to hunt you down, and eventually you confront her core and have to shut her off.

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Above: Portal spoilers

It’s a great twist to go from the repetitive, clean textures of the testing facility to the more varied and ramshackle feel of the Aperture Science building, and it’s legitimately thrilling as the game makes you feel like you’re on the run from a malevolent computer overlord.

As if that wasn’t enough of a high-octane climax, Valve sends us off with a charming, unforgettable song written by geek legend Jonathan Coulton and performed by GLaDOS, “Still Alive.” (See point #6.)

Portal 2’s ending hits a few similar notes, but manages to ratchet up the intensity even higher. When it comes time to shut GLaDOS down, you plug in Wheatley to take control of the Aperture science, but he turns on you. You plug GLaDOS into a potato battery (she has some choice words about this), and scheme with her to now take control back over from Wheatley.

At last you corner him in the server room, but he fights back. Just as it looks like you may be finished, the game gives you a clear view of the moon through the broken roof. When you fire a portal at it, everything in the room is sucked through the portal, except GLaDOS saves you at the last second.

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Above: Portal 2 spoilers

Finally, you escape the Aperture Science building through an elevator – which gives you a view of choir of turrets along the way – and you step into a peaceful, photorealistic field, free at last.

Like much of Portal 2, it’s bigger and better than what we get in Portal 1, if not quite so thrilling because we all kind of expected a badass ending. Still, I rank the two Portals near the top of any video game endings I’ve played.

4. (Portal 1) Length

One thing I loved about the original Portal was that it was so short. True, it left you wanting more, but in a good way — the experience was so rapid-fire and exhilarating that it never wore out its welcome.

It took me three or four hours to get through, which is a good amount. That’s either two decent sized play sessions or — if, like you me, you get completely sucked in — one super-sized session. Like two Samoas at the end of a meal, it’s just the right amount of indulgence.

Portal 2 took me two or three times as long, but the majority of the additional time is new story and exploration. It’s still a fun experience, but one that feels removed from the jolt that was Portal 1. Some of the wrinkles and variety of Portal 2 prevented it from feeling like a slog, but there’s no doubt Valve succumbed to the “more is more” that is normal in major video game design.

5. (Portal 2) Co-Op

But the biggest thing that Portal 2 has in its favor over Portal 1 is the incredible co-op mode. This blows open the puzzle design in a natural, intuitive, brain-bending way. It’s a great way to spend a few hours with a good friend (thanks, Hunter!), full of “you’re a genius, man!” moments as you solve puzzles together.

Yeah, the adventures of Atlas and P-Body don’t have the same charm or humor that the single player games do, but it might be the most fun I had with Portal 2.

6. The credit music

Both Portal 1 and Portal 2 have incredible, musical ways to say “thanks” and “farewell” to its players.

“Still Alive,” of course, was one of the best music-related moments in all of gaming of the 2000s. Like the game the preceded it, it’s packed with dark wit and a charming, unexpected pizzazz. Thanks, Jonathan Coulton (whom I previously knew for his cover of “Baby Got Back” — which later made headlines when Glee did a cover in his style without thanking him), and thanks, talented YouTubers for your many great covers.

“Want You Gone,” the closing song to Portal 2, is nearly the equal to “Still Alive” in catchiness and clever lyrics, but — like most of Portal 2 — feels a little bit like more of the same. More unexpected and fantastically brilliant is the “turret opera” just before the closing credits. It was one of the moments that gave me chills in Portal 2.