Scot McKnight on why the problem is the problem. That is, our gospel is too weak because the problem our good news addresses isn't big enough. You should read the whole thing, but to sum up, Scot points out that the biblical gospel addresses 4 problems:
1. A problem with God: fear.
2. A problem with Self: shame.
3. A problem with Others: enmity.
4. A problem with the World: exploitation/irresponsibility.
We've usually focused on just the first problem, with maybe a few jabs at the second. "The Gospel" usually means getting right with God (entirely thought of in legal terms) so you can be whisked away from the evil world. This is what Dallas Willard calls the gospel of sin management. It's good, but not good enough, and certainly not the robust gospel found in the Scriptures.
(Things I did not say: that Jesus didn't die for your sins, that a penal substitution theory of the atonement is wrong, that evangelical Christianity is bad, or that evangelizing is wrong.)