Observable's evaluation model confers a big advantage too - you're free to write the prose and define constants, variables and imports in any order you like. Multiple times have I been able to write some prose that reads well, but forces things to be defined in an order that is not the same as its evaluation order. And if I don't want anyone to see some code, I stuff it at the end of the notebook (often imports).

That aside, I completely agree - Observable has brought back a lot of the joy of programming I had when I first started. Congratulations to Bostock and the team.