"This is the Only Level" (TitOL) and "You Have to Burn the Rope" (YHtBtR) not only share a straightfoward titling scheme, but many of the same mechanics and even tone of message.
TitOL is unique in how it uses the exact same level, but has several stages where the way that the player has input and control over their elephant character change. The constant changing of how the game is played creates a bizzare dynamic where the player experiments with how he or she is meant to reach the end goal, turning what would as first glance appear to be a monotonous task into a interesting puzzle. YHtBtR meanwhile, starts with a long passage way prior to the final conflict: an allegory for the struggles that lead up to our true goals. Either that, or I'm reading in to it to much and it's a game commenting on how ridiculously easy some of the games of its era were.
Both TitOL and YHtBtR are both mechanically similar sort of. Sort of because TitOL changes its mechanics every stage but at their core they operate the same: jump over platforms, reach the goal. However, despite this simplicity it doesn't stop them from offering much more in terms of narrative.
Playing and observing gameplay are each unique and separate experiences, especially when the person you're observing has very different tastes in games than you do. I love Little Interno. It's a simple puzzle game where the core mechanic is burn things in a fireplace. Broadening that, you're meant to solve word puzzles by burning several objects together at once which awards you with more money to burn more things, and eventually the ability to buy more things so that you can burn more things. There's also a subtle and teased story throughout that gives the game an unsettling and mysterious tone.
The person I observed playing the game however, didn't appreciate any of these nuances. Admittedly, I don't really describe the game as being engaging but rather it's require submission. In both the aesthetic sense and literal sense. If you aren't willing to experience the game (accept its magic circle) then you aren't going to get back anything from the game. He really didn't enjoy it, and easily put it aside; clearly he wasn't interested in playing.
In this instance, I, as an observer, get nothing out of the experience if the person playing isn't experiencing the game themselves whether that be the game's fault or the player's fault.