Short song, but packs an unbelievable amount of awesome into the time you spend with it.
It somehow makes one of the most inspiring songs in the series be slightly depressing. A certain glitch Pokémon causes audio glitches, presented in the linked video as a simplified version of Route 4's music playing at Lavender Town's speed. You knew it was time to get serious when you heard it.
You step outside, you get your starter and you leave your little pokey town and venture into the world full of hope and ambition.