The final stage of Donkey Kong Jr. neatly embodies the gestalt of the entire game. It calls to mind the equivalent level of the original Donkey Kong, yet its familiar objects finds itself turned (literally) sideways to make use of Junior’s vertical agility.

You remember the final stage of Donkey Kong, yes? The construction site in which Mario collected rivets to cause the structure to topple, stunning Kong and allowing the hero to rescue Pauline? You’ll find echoes of that here, as Junior works to free his father and get the best of the villainous Mario. Rather than removing bolts, however, you’re instead inserting keys into locks that will unchain Kong. The logic of the level is a little odd, Mario having left the key for each lock hanging from the chain that particular lock binds down, but, you know… video games.

    

So we have eights chains and six locks. This stage sees Junior in his ideal element, as the action transpires almost entirely on chains spaced evenly across the stage. Gone is the troublesome platforming; once you hop onto the chains at the beginning, there’s really no reason to touch the ground for the remainder of the stage. As such, this level requires an understanding of Junior’s climbing mechanics, but once you do it becomes a joy to navigate: A test of your ability to assert dominances over the game’s control scheme.

Each key you slide to the top of the stage unlocks a portion of Kong’s chains. You can set yourself back if you’re not careful — an unused key can just as easily be pushed down as it can be lifted up — but thanks to the placement of the chains you’re actually better off pushing multiple keys at a time whenever possible.

The stage isn’t without risk; Mario releases birds that behave like the ones in stage two. Actually, they’re even more dangerous than in the previous stage. The other birds made a single U-turn upon reaching the right edge of the screen, but these continue to work their way back and forth, crossing the screen several times at different levels. They’re capable of flying at varied heights at each flight level, too, so you can’t count on any single spot of the screen being a guaranteed safe zone. You need to stay on the move constantly in order to evade the birds, several of which can be on the screen at once (this is where you encounter the risk of accidentally pushing the keys back down as you slide to stay clear of their flight path).

In addition to the lateral threat posed by the birds, Junior also has to contend with several of the Snapjaw traps that climb up and down the chains. These are the red variety, meaning they move more slowly and don’t respawn like the blue ones do — but also unlike the blue ones, they’ll double back at the end of a chain and climb back to the top of the screen, meaning you need to watch for danger moving toward you in all four directions. It’s a simple combination of challenges, but effective: Between the birds and the Snapjaws, Junior’s enemies create a thorough dragnet of danger that covers practically every inch of the screen.

Nevertheless, because it emphasizes the skill set around which the game is primarily designed, the final level is much less difficult than the second and third. That’s not a knock against the stage; on the contrary, it’s a good thing. Much of what made the earlier levels so difficult stemmed from the inconsistency and unreliability of Junior’s platforming controls, and the fact that the protagonist was so poorly suited to some of those situations. Here, we have a stage in which the game’s mechanical innovations are put to their full use, forcing you to fully grasp the differences between quick climbing (with a spread grip on multiple chains) and a quick descent (with a double-handed grip on a single chain).

It’s a great finale to the game, though the fact that this all-climbing scenario didn’t appear earlier is a real shame. It feels like Donkey Kong Jr. ends right as it’s finding its groove.

And that’s basically the problem with Donkey Kong Jr. in a nutshell. While it’s an admirably ambitious attempt at creating a sequel that didn’t simply coast on the success of its predecessor, it doesn’t live up to the high standard set by the original Donkey Kong. It lacks Kong’s purity of design and focus, adding new skills for the player to master. That’s a good thing to be sure, but Junior’s expanded repertoire comes at the expense of his core platforming abilities. He’s both clumsier and more complex than Mario, and the layout of several of the stages betray this fact with their unwillingness to let go of Donkey Kong‘s basic platforming structure.

While many of Donkey Kong Jr.‘s sequences play cleverly off scenarios from the first adventure, they lack that final touch of perfectionism that makes so many of the games surrounding it on either side of the franchise true classics. It’s a good game bordering at times on excellent — but it’s not at all the masterpiece its predecessor was.

Still, you shouldn’t write it off. It allowed Shigeru Miyamoto and his peers to experiment with new ideas, get a sense of what worked and what didn’t, and double down on the series’ strengths. Not coincidentally, many of its elements and concepts would show up further down the road.