na-adjective
wildly enthusiastic; crazy about
Describes intense passion or fanaticism for something, often used with な to modify nouns.
彼は熱狂的なサッカーファンだ。
He is a wildly enthusiastic soccer fan.
その歌手の熱狂的な支持者が集まった。
The singer's crazy supporters gathered.
夢中 means 'absorbed in' or 'obsessed with' and often describes a temporary state, whereas 熱狂的 describes a more enduring, passionate trait.
Compound of 熱狂 (nekkyō, 'wild enthusiasm') + 的 (-teki, '-like'). The base 熱狂 is from 熱 (netsu, 'heat') + 狂 (kyō, 'madness').