- no gender (le and la in French; der, die and das in German, etc.)
- no plural
- no articles (a, an and the in English)
- only three irregular verbs (corresponding to 'be', 'do' and 'come')
- only five vowels
- no diphthongs
- no consonant clusters (e.g., thrills in English)
So why is it considered a "difficult language"?
It is certainly different. For example, concepts such as politeness and probability are more important than in English. Often the subject is not expressed, so you have to make an intelligent guess.
And then there is the writing system. It is based on Chinese and the basic set now consists of
- hiragana (about 45 signs for writing grammatical endings and words that can't be written with characters)
- katakana (about 45 signs for writing foreign words and onomatopeia)
- about 2,200 characters (typically each character has two pronunciations - one based on the original Chinese reading (the on'yomi) and a Japanese reading, originally often a translation (the kun'yomi).