My biggest gripe about English is that there is no consistent relationship between morphology and part of speech. There is a muddy, approximate relationship which is inherited from French/Latin and German, so that for example you typically know that if you see an adjective X, and see a word Xity, then the latter word is a noun meaning "property of being X". Similarly, if you see an adjective Y, and another word Yen, the latter word is a verb meaning "to make Y". But this system is not used consistently. Ideally, a listener (reader) should be able to identify the part of speech of a word immediately by inspection of phonological (typographic) expression.

If you want to follow this rule, you will need to make it easy for people to do the sorts of colloquial grammar-jumping that come up in everyday speech. For example the word "hammer" is a noun but also a verb meaning "to hit with a hammer". "Ship" is a noun but also a verb meaning "to send by ship" and so on.

Another issue with English (and probably other languages) is that prepositions are overloaded, so that the same word can mean different things, as in "Galileo saw a man with a telescope". Since with can mean both by means of and carrying/holding, the sentence is ambiguous. It doesn't seem unreasonable to ask that every important case in which a preposition must be used should correspond to a distinct word.