Playful, Energetic, Sympathetic.
The tone of Love's Labour's Lost is strongly influenced by its setting: how can you be anything but cheerful in idyllic nature? These characters are on one long picnic/barbeque/camping trip.
Until the entrance of Marcade, an open feeling of fun and silliness pervades the play, which abounds with games. The characters play word-games with each other, exchange riddles, climb trees, play dress up, and tease each other relentlessly. Just check out Rosalind's good-hearted glee when she thinks of mocking Berowne:
ROSALINE: How I would make him fawn, and beg, and seek,
And wait the season, and observe the times,
And spend his prodigal wits in bootless rhymes,
And shape his service wholly to my hests,
And make him proud to make me proud that jests! (5.2.67-71)
Humanist satirist that he was, Shakespeare succeeds in making fun of all the characters while preserving our sympathy for them. For the most part, the characters are all likable. They are people we want to watch getting up to all sorts of nonsense... and we want them to succeed in the end.