Somehow it reminded me of the first Prince of Persia, nice idea making the collectables weighted. Could've used a restart button, nevertheless good first attempt.

Very cool use of the limitation, factoring weight into  platforming. Short, but not a bad puzzle. Great first effort. Also, the visuals are great.

A couple of suggestions:

-The main character should move a bit faster. When the movement is too slow, it feels frustrating for the player.

-Add some music and sound effects. A little bit of effort goes a long way in the audio department--even mediocre sound effects (as long as they're not too grating) make the game world feel much more alive. You can look into the utility bfxr to create old-school sound effects, and look in the Unity Asset Store for free music you can use in your projects.

Needs a way to restart when the mechanics are so punishing. Good job on making your first game though!