Here in Melbourne Australia, honestly, VicPol are fairly good and give us all a lot of leeway (they genuinely seem to want to keep us safe).
I know its not the same elsewhere though, but in general, the people here mainly complain about the police because
The complainer is an asshole, or genuinely do a lot of dodgy stuff and deserve it. Generally Meth heads, or shitty disrespectful drivers
The only other complaint I've seen is that they don't solve someone's problem (like recovering stolen bikes). But, that sometimes isn't easy and can't really blame VicPol