I'm really glad to see this thread. When I first joined PF, I noted the comparative absence of MacDowell. Several reasons came to mind. First, MacDowell was more popular when more people played the piano; I say this because my grandparents were music teachers in the 1920s-1940s, and everyone was playing (or seemed to be playing) MacDowell. Second, he does have a "USA" character, some of the time at least, and this may be alien to some tastes.
At any event. I second what's been posted here. Witches' Dance, Shadow Dance for sure. Puritan Days (in the initial post) and the rest of the opus that contains it, New England Idylls.
Some additions. Wild Rose is still played a fair amount, but I'd add the rest of Woodland Sketches, especially Water-Lily and Uncle Remus. Then there's the Six Poems After Heine, which contains Scotch Poem, my own favorite -- but the other pieces in the collection are well worth investigating. Scotch Poem is available separately from many publishers and used to be very popular. This is one of the pieces MacDowell revised -- after comparing the editions, I think the first is the best; the revisions of the second are, well, fussy. But you should probably look at both. Sea Pieces is another good collection; I'm especially fond of Wandering Iceberg and To The Sea.
None of these are technically outrageous, but I think many people can play, say, Wild Rose technically before they're ready to get out what's in the music.
All of the pieces I've mentioned are in print. MacDowell wrote a lot else for solo piano, and I've yet to find a piece I regret playing. The other pieces require a fair amount of tracking down.
If you've got the Dover volume of music from the Etude Magazine, there's a MacDowell piece there with performance comments from his widow.
Finally, James Barbagallo recorded 3 cds of MacDowell. For my taste, his tempos are often too brisk, even in pieces which require speed.