Doppler is a very quick arcade title of escalating difficultly. Reading an explanation of it's gameplay would take longer than actually playing a round, so I would heartily recommend playing said round here.

From a design perspective, Doppler was designed to be produced in 3 hours, for the 59th Trijam. That initial constraint forces the question "how small a number of elements can create the experience of a game". How many animations, characters, sounds, scripts, and behaviors can you not make, and then still spark a response in the mind of the player.

There are, of course, a lot of answers. But mine is this many:

About 9 assets controlling how the circles behave and look, and 1 scene file to host them.

A layer above that sheer technical detail, the game is essentially a dialogue between the player and the single mechanic of the circles...

dopplers? dops? I'm going to say dops.

Right, the game is a conversation with the single mechanic of the dops. The core challenge is in identifying which of them is closest to overflowing and ending the round, and then hitting them quickly. The car horn with the titular Doppler effect is the core indicator of how close to defeat the player is. The core aesthetic is contained in the dops clear pastel color, and in the bass thud whenever they spawn or de-spawn.

This insultingly simple game delivers an experience because of it's focus on this conversation of player input and the game's audio/visual feedback.

If I can put on a design theory hat for a second, there is a lesson in design hiding in this tiny experiment. You could force a lot of games through the filter of "a player and a single mechanic talking".

Some games would essentially cease to function. Imagine a build of World of Warcraft where the player could only click to move their avatar, or a build of any Final Fantasy title with only the combat menu; either ceases to be anything like game that the full builds are. Even if we were to cherry-pick the higher level mechanics that play to these games core engagements, you would likely end up with an extremely bare bones visual novel or something resembling the old parody Progress Quest. These games don't survive being paired down to single mechanics.

But imaging a build of Doom where the player can only fire their weapon, or LUFTRAUSERS where the player can only control their aircraft feel different. The game is still giving players significant feedback, and is still delivering a version of the fantasy that game promised. The basic feeling of power or agility are still there, and these primitive games still function.

One possible conclusion being, that even in games who's focus in on something other than the second to second feeling of gameplay, that you can only derive more engagement from improving that basic player-mechanic conversation.