I think there are two types of people in this world: those who know Spanish or a similar language, and those who don’t. People in the second group will usually know English. In all cases: a lot, or just a bit.
Both groups will have their reasons to dislike Interlingua.
To those who know Spanish, Portuguese or Italian, Interlingua will seem somewhat silly and childish at first sight. Not like a serious and fully functional language. That’s because it has no verb conjugations, and no explicit personal pronouns.
‘I read’ or ‘I am reading’ in Spanish is ‘leo’. ‘We read’ or ‘we are reading’ is ‘leemos’. There’s no need to use the personal pronouns ‘yo’ and ‘nosotros’, because they are unambiguously implicit from the verb forms.
French does use personal pronouns, but it also has conjugated verb forms, at least in writing, although many of them are homophones.
The Interlingua translations of the above examples are ‘io lege’ e ‘nos lege’. Always with the personal pronoun, and there are no -o or -mos endings in sight.
‘Le lingua’ is Interlingua for Spanish ‘la lengua’. Interlingua, like English, does not have grammatical gender, there are no feminine and masculin words, so the definite article is always ‘le’. That sounds and looks weird and silly to Romanophones’ ears and eyes.
Another strange thing: Interlingua uses -va for the past tense throughout, while in the other languages, those forms are only used in special cases, as an imperfect tense, while the somewhat irregular past forms are more usual (except in spoken French). But they don’t exist in Interlingua. ‘I sang’ is usually ‘canté’ in Spanish, but Interlingua has only ‘io cantava’ (cognate with ‘cantaba’) and ‘io ha cantate’ (like ‘he cantado’).
But if you manage to look beyond these initial effects, and read more in Interlingua, and even try to use it yourself, you will find that like any language, Interlingua has a unique character, a look and feel of its own, and an intrinsic beauty and charm. It is not Spanish or Italian, it is Interlingua.
Thus it is possible to like it for its own sake. Or at least that’s what started to happen to me in late 2013 and early 2014. Doesn’t mean I now like the other languages any less.
The other group, those who know some or a lot of English, will initially find Interlingua hard to understand, because they miss a lot of function words. Interlingua function words are often similar to Spanish, and sometimes not even that, in which case they were supplemented from Latin.