Sentimental means easily moved by memories and keepsakes. Sentimental about it, sentimental value, hopelessly sentimental.
Sentimental value is the fixed phrase for something worth little and kept anyway, and it is a complete answer to any question about why. Applied to writing or film, sentimental is a criticism meaning manipulating feeling cheaply — sentimental is what you call somebody else's emotion. Note sentiment, which means both a feeling and, in the plural, opinions; and sentimentality, which is always negative.
1adjectivesentimentalEasily moved by memories and keepsakes.
“She's very sentimental and keeps every birthday card she has ever received.”
2adjectivemanipulatingManipulating feeling cheaply.
“The film was cheaply sentimental, with a dying puppy and swelling violins in every scene.”
sentimental is a quality of feeling.
Proto-Indo-European
*sent-
Latin
sentimentum
Old French
sentement
English
sentiment
English, today
sentimental
From sentiment + -al. sentiment comes from Old French sentement, from Latin sentimentum. From Old French sentement, from Latin sentimentum.
Etymology from Wiktionary, CC BY-SA