I’ve been reading an old article by F.F. Bruce, “When Is a Gospel Not a Gospel?” BJRL 4 (1963): 319-39. Bruce concludes with this:
To sum up, then, we may say that, according to the general consensus of the New Testament teaching, a gospel is not a gospel when:
1. It is detached from the Jesus of history;
2. It gives little or no place to the passion;
3. It exalts human achievement in the place of the grace of God;
4. It adds other conditions to the one which God has declared acceptable (even if those additions be things good and desirable in themselves); or
5. It treats righteousness and purity as things which the truly spiritual man has outstripped.
1. It maintains contact with the Jesus of history, affirming that “this same Jesus” who came in the flesh and died is the vindicated and exalted Lord;
2. It embraces and proclaims “the stumbling block of the cross”;
3. It extends the grace of God to men for their acceptance by faith;
4. It relies upon the power of the Spirit to make it effective in those who ear it; and
5. It issues in a life of righteousness and purity which is sustained and directed by the love of God.
I think is pretty good, accept there is no concrete connection to the narrative of redemptive-history, resurrection needs a mention, and for christology we have the mere fact of Jesus’ earthly existence rather than linking his messianic career and passion together.