A lack of sentimentality ultimately seemed bad (2-4)
I believe the answer is:
no good
'bad' is the definition.
(similar in meaning)
'a lack of sentimentality ultimately seemed' is the wordplay.
'a lack of' becomes 'no' (lack of money is no money).
'sentimentality' becomes 'goo' (informal term for sentimentality).
'ultimately' indicates one should take the final letters.
The last letter of 'seemed' is 'd'.
'no'+'goo'+'d'='NO-GOOD'
(Other definitions for no good that I've seen before include "Useless, not worth bothering about" , "(Of a person) beneath contempt" , "Hopeless" , "worthless sort" , "Futile; worthless" .)