Really like to love a lot of Fleischer's work, the mid/late-30s Popeye cartoons, some of the earlier "Color Classics" cartoons and pre-code Betty Boop (the Koko cartoons too) being some of their best work. It was very sad though drastically that they declined drastically in the early 40s, but although none of the 40s Fleischer Popeyes came close to the best of their previous work they were still a lot better than most of their output from this period.
That is true for the cartoon that started off the 1940 output 'Shakespearian Spinach'. Far from being among the studio's best work, but not indicative of their decline or anywhere near their worst (the "Stone Age", "Animated Antics", the worst of "Color Classics" and Gabby cartoons are much bigger indicators of all that). While not considering it a great cartoon, still consider 'Shakespearian Spinach' a pretty, well worth watching one with a lot to like.
Am very mixed on the voice acting. Have no problem with Jack Mercer, he is the definitive voice actor for Popeye. Margie Hines though never seemed to be the right fit somehow for Olive, not having Mae Questel's charm and the character design is suggestive of a younger-sounding voice needed. Had more of an issue with Pinto Colvig (like him though in other things), who is just not sinister-sounding enough for Bluto and somehow it was difficult to forget that this was the original voice of Goofy voicing this larger than life and both menacing and funny (he does funny well, not so much the menacing) character.
Maybe it could have benefitted from a tighter pace.
However, the animation is neatly and expressively drawn (especially with Popeye) and still very much like the work that goes into the backgrounds. The music, appropriately like its own character, is as beautifully orchestrated and characterful as ever. The dialogue is a lot of fun to listen to, most of it sung and the lyrics at their best are quite genius. Olive for a while did not have material this funny than when she is with Bluto.
While there isn't really anything that one calls hilarious in 'Shakespearian Spinach' it is still worth seeing to hear Olive's lyrics, see Popeye as a woman (quite a picture) and to see Shakespeare being hammed up so entertainingly and brilliantly for any cartoon. The story is not much new but still a lot of energy. All three characters are handled very well.
Summarising, pretty decent for Fleischer's weakest period but not one of the best of the series. 7/10