[decode]

While I agree with you in general, a surprising number of grammatical features that make many other languages difficult to learn are missing in Indonesian. Some examples:

No grammatical gender

No plural forms of nouns

No grammatical case

No verb conjugations

No verb tenses

In addition, written Indonesian uses the Latin alphabet and has a very consistent phonemic orthography.

Of course, it also has some more complicated features, like formal and informal pronouns. But it still seems fair to me to say that it is grammatically simpler than many (most?) other spoken languages.

[tikwidd]

I don't think that is fair to say. There are lots of other languages that lack most/all of these features (e.g. Mandarin has no gender, limited number marking, no case marking, lack of inflections). Indonesian is not unique in that regard.

Indonesian verbs lack the tense, number and person agreement marking that is commonly found in European languages, but they have a lot of derivational morphology including complex voice and valency operations (Austronesian alignment[0], causatives, applicatives etc.)

Indonesian also has noun classifiers like Mandarin which have to be memorised like grammatical genders.

[0]:https://en.wikipedia.org/wiki/Austronesian_alignment

[perlancar3]

Yup, typically what a native Indonesian would say about how easy their language is. But foreigners are often tripped with other aspects of the grammar, which the native take for granted, such as those tikwidd mentions: noun classifiers, morphological derivation, a high number of prefixes/suffixes/infixes and their combination, lack of cue on how to pronounce the different "e" vowels, etc.