I really like the Heart of Greed, it's a great item. It's basically an encounter when it's used that has several layers of depth from its breif description.
The visual imagery of the iron grates frozen and having to push one's way through it is vivid and interesting. Also potentially useful to split the party for a little while.
Based on the description at the beginning of the adventure, I expected more treasure in the well. Is it because one is meant to lament their own greed drawing them down the well?
I like the variation in the flying skulls, but the encounter doesn't feel dangerous. I suppose that not all encounters need to be dangerous, but it seems warranted here. Even the Lich has been robbed of all of its abilities. If I ran this, I would still use a crippled Lich, but maybe give it some ability to threaten the PCs.