The song's mood doesn't become too happy or sad. You played melodies that would sound happy or sad with certain chords, but you used different chords, so the listener doesn't get the expected satisfaction. For this reason, for me, the song symbolizes apathy.
I love the rhythm change at 2:42.
The chords you used in this piece remind me of the music I listened to as a child, so it brings back memories that are rarely recalled. Major scales were rarely used, and songs of all emotions had diminished chords.
This is a great song for the end of the year :D