Moving, but maybe still depressing?
So warning of spoilers, but Arthurs sole mission is to find the place he is supposed to visit, before he can finally die. (His only wish because his girlfriend vanished from existence)
And in the end he finds the place, which is not what anyone expected and they indeed all die, including his daughter.
After they concluded, there is no other place, no other home, because, every other place is also falling apart. Pretty dark ending in my opinion.
But I also don't hate the ending of "Mostly harmless". It is a fitting end alltogether. Absurd and dark, just like the very beginning of the books are.
That apart, have you read the Dirk Gently books? I think those are DA's best, and I've happily re-read them multiple times.
I remember the 4th and 5th books as pale shadows of the others. I got the impression they were only written for the money.