Returning though, what he usually finds is a world of arrogance and hypocrisy; one where the people assume that living in a town devoted to Compassion means that they must of course be compassionate, and never mind whether or not they've just kicked out the poor and disenfranchised to a sewer town where even charity comes with a price.
This is of course sometimes part of the story - in the case of Ultima VII for instance, the population is being misled by an evil cult called the Fellowship and the psychic power of the Guardian, while in Ultima IX there are giant columns actively subverting the Virtues.
If we assume that the Avatar is also the Stranger From Another World who starred in Ultima I-III, Ultima V is also his fault, the Shadowlords and their brutal dictatorship having been spawned from shards left behind by his earlier monster hunting.
He takes over Britannia and enforces the Virtues with an iron fist that turns them into tools of tyranny rather than merely aspects of the three cardinal principles of Truth, Love and Courage. Dubbed The False Prophet, it sees the Avatar returning to Britannia and immediately being set upon by a demonic looking group of gargoyles who have been terrorising the realm.
You're assigned to take care of them, as heroes do, and that works for a while.
From there though, the series began getting more involved.
Ultima V for instance, while adding in a trio of evil called the Shadowlords, was narratively based on the subversion of those virtues - that there's a difference between the spirit and the letter of the law, as shown in the form of Lord Blackthorne.
It's just fascinating to me how the series that set out to hail the Avatar ultimately... To see what a failure the Avatar truly was, you just need to look at the point of the whole enterprise in the first place. In Ultima VII for instance, you know from the very start that the world is under siege by the machinations of The Guardian, but the one time he even acknowledges his existence is if you cast a spell called Armageddon - and even then, only to muse (as one of the few people powerful enough to survive that spell) that at least now he might not want Britannia after all. you can also find out that he's knocked up one of his maids. Anyone could in theory be an Avatar (if not of course complete the exact same quest, since that's done and dusted), and even if most won't have what it takes, they can at least aspire to it - to step up, to be better, to actively live the Virtues instead of simply paying lip-service to them.. But when he's gone, and as said, he can be gone for centuries at a time, does anyone truly follow in his footsteps or rise to the challenge? They figure that if something goes badly wrong enough, he'll be back.