As I've said before, there are songs on this list that I'm positive are objectively great, while others probably aren't that great, but I like them anyway. This is in the second camp.
Then I forgot about it for about 20 years, until I decided to listen to it again on a whim, and you know what? It's not an awesome song. It's cheesy and synthified, and sung with complete earnestness, and it's a little hard to take solo Peter Cetera seriously in general.
The thing is, I don't know that in general terms, "After All" is any more cheesy than any of a billion other classic 1980s duets: "Up Where We Belong" or "Somewhere Out There" or "Total Eclipse of the Heart." And all of those are universally beloved, at least on an ironic level, so maybe I shouldn't feel weird about liking this song this much. There's nothing quite like a good slow dance song, and "After All" is as slow-dancey as it gets.