Learn Hardcore Japanese: watasi ha susi ga suki desu.

は is the topic marker. It tells us that the sentence is about 私 (I/me). Once “I” is set as the topic, the rest of the sentence provides information about that topic.

Why is 寿司 followed by が instead of を?

Because 好き is not a verb but a な-adjective expressing a state (“to be likable”). In Japanese, the thing you like (寿司) functions like the subject of that state and is therefore marked with が. The object marker を is reserved for true verbs of action, which 好き is not.

What part of speech is 好き? Is it a verb?

好き is a な-adjective (sometimes called an adjectival noun), not a verb. To make it a predicate, you attach the copula です (or in plain form だ):
– Polite: 好きです (“is likable”)
– Plain: 好きだ
When you modify another noun directly, you add な, e.g. 好きな映画 (“favorite movie”).

What is です doing at the end? Can I drop it?

です is the polite copula (roughly, “is”). It turns your statement into polite speech. In casual speech you can switch to the plain copula だ:
– 私は寿司が好きだ
Or even drop it altogether in very informal situations:
– 私は寿司が好き

Why can’t I say 私が寿司が好きです or 寿司を好きです?

You can’t have two が markers in one simple clause; one should become は if marking the topic.
好き isn’t a transitive verb, so it doesn’t take を. The fixed pattern is:
[Topic は] ＋ [Thing が] ＋好き (です).

Can I omit 私は and just say 寿司が好きです?

Yes. Japanese often drops topics when they’re understood from context. 寿司が好きです naturally implies “I like sushi” if you’re the speaker and no one else is under discussion.

How is 私は寿司が好きです pronounced in hiragana and romaji?

In hiragana: わたしはすしがすきです
In romaji: watashi wa sushi ga suki desu

Why is 寿司 written in kanji rather than hiragana or katakana?

Many Japanese words—especially common nouns and food names—have standard kanji spellings. 寿司 is the usual kanji for “sushi,” though you might also see すし (hiragana) or スシ (katakana) depending on style or emphasis.