Sentimental, romantic, mawkish, maudlin, soppy, mushy, slushy are comparable when they mean unduly or affectedly emotional.
Sentimental usually suggests emotion that does not arise from genuine or natural feeling but is evoked by an external cause, by a particular mood, by an excess of sensibility, or for the sake of the thrill, or is merely an affectation that is temperamental, the moment’s fashion, or designed to achieve an end.
Romantic implies emotion that has little relation to things as they actually are, but is derived more from one’s imagination of what they should be ideally or from one’s conceptions of them as formed by literature, art, or daydreams.
Mawkish, when it implies sentimentality, suggests a kind that creates loathing or disgust because of its insincerity, emotional excess, or other signs of weakness or futility.
Maudlin stresses a lack of balance or self-restraint that shows itself in emotional excess (as unrestrained tears and laments); usually also it suggests extreme or contemptible silliness.
Soppy, mushy, and slushy come close to mawkish in their suggestion of distasteful and disgusting sentimentality.
Soppy (chiefly in British use) often carries a strong suggestion of silliness in showing affection.
Mushy may suggest softness or wishy-washiness.
Slushy applies chiefly to utterances or personalities that are so sentimental or emotionally confused as to seem senseless.