I am a Catholic, I tend to think everything the Pope does is good, and I suppose theologically I would describe myself as a Ratzingerian, so I do not normally criticise the Pope and I trust his judgement but at the heart of the Pope's theology is "both and" rather than "either or". So having suggested some very good reasons for the Pope to resign rather than die in office let me present a few contrary arguments.
The Pope's resignation sets a precedent, it presumably means his successors are now likely to resign when they feel unable to continue. If future generations are likely to live to over a 100 we could end up with a small gang of past Popes living in the Vatican gardens. What is the collective noun for a group of Popes?
The precedent also means that other bishops are more likely to resign if they feel they are declining before they reach retirement age. In the case of those bishops who hate being a bishop and tell everyone it could be a good thing but it is not always the case.
If Popes are expected to retire rather than die there will be an increased pressure on future Popes by factions in the Curia to go, not so much when they want but when they are pressured to do so. Anti-Pope factions are likely to think it worth building up pressure on a Pope or his household to force him out, so too is the world's media..
The retirement of a Pope seriously undermines the ancient notion of the mystical marriage of a bishop to his Church, which contains in it the idea of the esse of a bishops relationship being more important than agere. What he is in relationship to his diocese until VII was considered to be more important than what he did, it seems to come from deep in the heart of Catholic/Orthodox Tradition, it could be argued it goes back to the Apostles, hence the Orthodox hatred of "desiring other Thrones", which in the East is seen as kind of simony. Thus I have a little sympathy for Cardinal Dziwisz' remarks about Pope John Paul not choosing to get down off the cross. Putting up with a bishop for better or worse, in sickness and health, until death do us part is or at least was of the marriage. The relationship with a bishop and his diocese is about a relationship of mutual cherishing, not one of pure functionalism.