"neither disappointed" is correct and usable in written English.
You can use it to express that two people or more have not been disappointed by something. For example: "Neither Sarah nor John were disappointed by the restaurant's new menu."
I'm neither disappointed nor cynical.
Reese said that he was neither disappointed nor blindsided by Smith's sudden departure.
All the right players lined up for the Royal Ascot equivalent of the 2000 Guineas and the 1000 Guineas Classics, and neither disappointed.
Although the Giuliani administration has not yet given Mr. Levy a pat on the back, he insisted that he was neither disappointed nor frustrated and said that in fact, his relationship with City Hall "is building".
Venue: LES BOBARDS The afternoon showcase of talent, starting around '16 h', brought us the opener Ventanas, spilling a mixture of Bulgarian, Greek, Turkish and Sephardic songs of amor that had me neither disappointed or blown away, or even moved.
David Robinson, writing in The Times observed that Licence to Kill "will probably neither disappoint nor surprise the great, faithful audience", but bemoaned the fact that "over the years the plots have become less ambitious".
"Drink to Me Only," though marvelous, is such a mixture of formality and informality, so open about displaying the nuts and bolts of its movements and its construction, that it makes you ask, "Where's the theater in this?" In an opposite way, "Rodeo," with no pointwork and few conventional academic steps, invites you to wonder, "Where's the ballet in this?" Yet neither disappoints.
Neither dish disappointed.
Neither defense disappointed, but the Texans were just that much better.
This was an opportunity for the Qualifiers' two fairytale stories to take centre stage and on an afternoon when victory perhaps had greater importance for affairs off the field, neither side disappointed.
