As someone whose ministry required him to visit in different churches nearly every week for 14 years I've had the opportunity to hear a lot of sermons from many preachers. The best messages I heard had two qualities. They contained both exposition and application.
There are some pastors today who believe that they have to water down the gospel if they want to reach new (often younger) people. Nothing could be further from the truth. Numerous studies have found that young people and unchurched people are not turned off by biblically sound messages. In fact, they want to hear such sermons. I would encourage you to read The New Faithful: Why Young Adults Are Embracing Christian Orthodoxy by Colleen Carroll and Surprising Insights from the Unchurched and Proven Ways to Reach Them by Thom Rainer for more on this.
But, sound exposition is not enough. There must also be application. As a pastor there were times I would finish preparing a sermon, read it, and then throw it away because it didn't answer the "So what?" question. There was nothing wrong theologically with the message, but it didn't compel anyone to do anything. As pastors we don't want to be content with sending people home from a worship service inspired to eat lunch. We want to challenge people to do something as a result of what they have just experienced and heard.
In one of my favorite books, Jim and Casper Go to Church: Frank Conversation about Faith, Churches, and Well-Meaning Christians, Jim Henderson, a Christian, pays atheist Matt Casper to attend 12 churches with him and then write a book about their experiences and observations in each of these churches. At the end of their experience Casper's primary question was "Jim, is this what Jesus told you guys to do?" It seemed to him after visiting some of the best-known churches in America that the only thing Jesus wanted his followers to do was to have church services.
Casper was looking for people to be challenged to action because of what they claimed they believed. He felt that asking people to "follow Jesus" wasn't enough. He was looking for concrete application. "Because we believe this to be true we should be doing...."
Exposition and application are both important if we want to preach messages that will change people's lives. Leave either one out and we shortchange our hearers. On the other hand, if we make sure to include both in every message we will grow our church spiritually and, often, numerically as well.