I don't know if a big intrusive text box is the best idea though. I think if something like this were to come along it should be similar to the piety tab in the lower right. That way every time one of you character stats changes (due to a pick up, god boon, weakening, level up etc it could be detailed in the bottom right, taking all the guess work out of where your stats are coming from.
I think something like this would be incredibly useful, especially if patches is along giving you damage bonuses (or whatever he does) you can have a log of where that comes from.
The only thing that would need to be exluded from the panel as far a stat changes would be damage taken and mana used.
I think this solution is smaller, less intrusive, and more informative than a huge congrats banner every level up

On the other hand I have no idea how long it would take to develop such a thing, or even if it is ultimately "desirable". I know I would like it though, so I could see the exact level gains and figure out where all my benefits are coming from.