That guy is quite smart, but doesn't have much of a personality.
He is quite an intellectual, but he lacks depth of character.
ーThat guy is quite smart, but doesn't have much of a personality.
「あの人はかなり頭がいいけど、薄っぺらいやつだ」
smart で「頭の良い・賢明な」
doesn't have much of a personality 「個性・魅力をあまり持っていない」＝「薄っぺらい人」と言えます。
ーHe is quite an intellectual, but he lacks depth of character.
「彼はかなりの知識人だが、薄っぺらいよね」
intellectual で「知識人」
to lack depth of character で「人格の深さに欠ける」＝「薄っぺらい」とも言えると思います。
ご参考まで！
カナダ 
