III is ok but I wouldn't say it's bad. At least not as bad as TMP and V. There's always people being contrarians about movies though. The general consensus is that TMP is super boring.

Of course everyone has their own taste. Maybe some people like how slow TMP is. It's a very different movie from the Abrams series so I wouldn't automatically invalidate someone who liked it but not the new ones. I can't stand Abrams' hectic/ADHD filming style so I've never liked his take on ST. But that doesn't mean the old ones are all good, the TNG movies are basically all trash except for first contact.