Kyoto has four very distinct seasons, and your experience of the city will be utterly different depending on which one you pick. Cherry blossom (sakura) peaks in late March to early April and is as beautiful as everyone says — the Philosopher's Path, Maruyama Park and the riverbanks of the Kamo are the classic viewing spots — but the entire country converges on Kyoto for a fortnight, and hotels book out six months in advance. Autumn foliage (kōyō) in mid- to late November is, if anything, even more spectacular, with the maples of Tōfuku-ji and the Arashiyama hills turning scarlet; again, book well ahead.
Summer is hot, humid, and exhausting — Kyoto sits in a basin and temperatures regularly push past 35°C in July and August — but it is also the season of the Gion Matsuri (Kyoto's great month-long festival culminating in a parade on 17 July) and the open-air dining platforms over the Kamo River. Winter is cold but rarely snowy; the city is at its quietest and cheapest in January and early February, and a dusting of snow on the temples is rare but unforgettable. If you want to avoid the worst crowds, late May and early June (before the rainy season) and early October are the best quiet-shoulder choices.