Their raw talent: The raw and undeniable natural musical ability in terms of their vocal abilities and songwriters of John Lennon and Paul McCartney was undeniable
They had a unique music style combining catchy lyrics with rock and roll: George Martin saw potential in this combination. While it wasn't new it seemed unique enough for it to work.
The energy : George Martin describes the feeling in the room from their performance as having electric excitement in 2 hours which he has never come across.