Personally, I have mixed feelings about Farage.
I think he's a good politician who's gifted at convincing people of his point of view (and making them think they had that idea all along); however, I dislike his anti-free-trade rhetoric and his passive acceptance of racism within his party, even if he himself is not racist.
I agree with a lot of what he says - I'm a Leave supporter - but I didn't want to Leave for the same reasons Farage did. I recognise the needs of immigration, and I love the idea of the Common Market. What I don't like is that centralisation and ever-closer union of the EU (I know we were exempt from that, and tbh the idea that we'd be further secluded from where most decisions are made is what really made me want to Leave).
Most of the people who dislike Farage do so simply because they can't actually be bothered to look at the context of what he says, or even look up what he says; all they think is that UKIP is 'racist', so anything associated with it they will hate.
Other people who hate Farage do so because they look at the context. If Farage talks about closing off the borders and putting Britain first, and this is a person who is an immigrant, or hates nationalism in any form, they'll dislike him because he goes against what may be some of their core beliefs.
Of course, someone may like Farage for the exact same reason - they think we should close our borders and put Britain first, so they like him even if they don't agree with many of his other economic principals.
It's impossible to thoroughly explain why every single person who dislikes Farage do so, but I like to think I at least touched on the main reasons.