The header to this post is a bit misleading, at least to some. While it is true that Jon Paul II is but one Pope in a long line of Pontiffs, to anyone under 30, he is effectively the Pope; the only one they have ever known. I vaguely remember the brief pontificate of JPII's predecessor. I recall more easily the media coverage surrounding the choice of JPII himself.
JPII did an admirable job of navigating the Roman Catholic Church through a time of massive change. Arguably he is responsible, with his many travels, for keeping the Vatican relevant in world affairs. Had he chosen to be anything other than the world traveler he was, it is doubtful, in my opinion, that the Vatican would have maintained its prominence. By visiting so many of the Roman Catholic faithful in their homeland, he established a more personal connection, I think, with the faithful.
His success in that regard may also be attributed to good timing, something all "great men" need in order to become great. A Pope from the former Eastern Bloc nation of Poland, he supported Lech Walesa during the days of Solidarity, which was perhaps really the time when the Berlin Wall fell, for all that it remained standing for some years after.
For all that John Paul II was a statesman and (perhaps inadvertently) something of a populist leader, his greatest success and greatest failures remain in the realm of religion. In terms of successes, we may note the stand for life, and biblical sexuality, for example. However it is the failures which, in my judgment, stand out. Under his papacy, Mariology has grown in breadth and depth, long past the point of being healthy. Under his papacy, syncretism, the blending of Christianity with other faiths, was unaddresed. Under his papacy ecumenicity was more with other faiths, like Islam, than with Christians (I recall his words about cultists, referring to charismatic protestants in South America).
I look at the approaching new papacy with some concern. JPII, for all his faults, had, in recent years, become innocuous, or at least a known quantity. It is unknown what his successor will do. If he is a conservative, then we can expect more of the same, perhaps at an accelerated pace. If something else... Well that is really unknown territory.
Praise God that He knows the future. Praise Him also that we have a High Priest (if not a Pope) who lives forever to intercede for us. (Hebrews 7:25).