Charming comes to mind: very pleasing; delightful. (The synonyms of this word attest to its strength: beguile, bewitch, captivate, enchant, entrance, fascinate.)
He could charm the birds out of the trees.
Charismatic: possessing an extraordinary ability to attract. (Again, synonyms attest to its power: charming, appealing, attractive, influential, magnetic, enticing, alluring. With her striking looks and charismatic personality, she was noticed far and wide.) This word has been associated with Christian denominations, however, decreasing its appeal to some.
By virtue of his charm and charisma, Kennedy overcame anti-Catholic prejudice to win the presidency in 1960.
The closest word that matches your description is lovable.
Inspiring or deserving love or affection
A lovable person is, by definition, easily and therefore quickly loved--though not necessarily by everyone, as not everyone loves lovable people. You would have to add additional words or phrases to say a particular person is unanimously loved.
Here are some quotes from Google Books showing its usage:
"Mary was extremely lovable!" Jane burst out angrily. "She had more...natural charm than anyone I've ever met. Everyone loved her--you couldn't help it." (Reveley, "The Etruscan Couple, and Other Stories")
"That commitment is not arbitrary, but the natural consequence of the conviction that God is love, that everyone is loved by God and that everyone is thus lovable." (Søren Kierkegaard, Eighteen Upbuilding Discourses)