Try to tell him “why” as best you can.
As a pastor it's very common for people to say it's bad or good but not give any details. Especially when someone criticizes your preaching the feedback is often meaningless stuff like “not being fed.”
If you say it's too hard to follow, the topic is dull, he looks too ugly and its distracting, you don’t like his smug attitude, he's smelly, he's not as good as the radio guy, etc. he just might be able to do something about it and improve.
So when you want to tell him what he's doing right, give him a good hint like “I followed it well” or it kept me engaged/ I connected with X, Y, Z.
Because the truth is there's many ways to preach that all work by and large. Yet even most the famouse preachers have a way that someone just don't like. Someone will even hate a great preacher’s very best sermon ever because his tie didnt match his suit/ or the stories were too long/ he didn’t do an altar call or did or didn't proof text. Or he's not their favorite preachers clone.
So the pastor has to adapt to his people when its not a matter of scriptural fidelity or something. And that's not exactly a matter of skill. It's a matter of him being told what people connect with. People themselves change to so they may wake up one day and hate what they liked.
Which is why criticism without details or made “spiritual” (I didnt feel it) should even treated as just hostility. “I don't like it… but won't even tell you why… so fix it for me without me telling you how.” Your pastor (as all of them) does get that kinda feedback. Even if it was the best sermon ever and it was just the wrong one for somebody. It's like saying someone is a sinner but you can't name or prove any sin.
So to say “I like it and here is why” is a compliment that doesn't just sooth him, it actually helps him know he's working in the right direction. Trust me he never ever hears that and needs to. Its human nature to feel “They are mad and I don't know why… but I want to fix it so lets try to make them happier by guessing” and that's not gonna make for very good sermons!
So if he hears “they liked X,Y,Z” he knows that part is working. It's an art form to preach to a specific church well. Some pastors even can't ever connect to a given church when they are great preachers in another style.