I only heard him speak a couple of times, and I have virtually no recollection of what he said. However, his writings have had a major impact on me. His Basic Christianity was one of the first books I read after becoming a Christian, and it helped clarify for me just what I had committed myself to. Later I was very influenced by his The Cross of Christ, and I have always enjoyed the lucidity of his contributions to The Bible Speaks Today series (particularly his exposition of the Sermon on the Mount). For me, three things about John Stott stand out: his clarity, which was the product of a first-class mind that had struggled long and hard to articulate the mystery of the gospel; his eirenic attitude towards those who disagreed with him (perhaps illustrated most clearly by his lifelong allegiance to the Church of England); and his willingness to espouse positions he believed to be biblically warranted regardless of the conventional wisdom among other evangelicals (e.g. his belief in annihilationism).
In the Time article mentioned above, Billy Graham summed up his life in the following words:
I can't think of anyone who has been more effective in introducing so many people to a biblical world view. He represents a touchstone of authentic biblical scholarship that, in my opinion, has scarcely been paralleled since the days of the 16th century European Reformers.