It is so good. Unlike the Ottawa Senators, you've figured out how to navigate the O-monogram issue (though to be fair, the A's have an easier path to it than the Sens do). The Old English O in the Oakland script is a perfect example of a small change that makes a big difference. Kelly green is beautiful, especially on the alts, and the Athletics home/Oakland road/A's thirds is the perfect distribution because of how the colored jerseys call back to the old Finley A's. The classic home hat on the road, an obvious fix. And the white elephant is white again! You'd think this would never have to be an issue in real life, but then again there are the "Big Blue" New York Giants wearing a preponderance of red, white, and grey.
I think I like the wider A better (and in turn, I like this middle way better than the narrow one that the A's use sometimes) but it's the kind of modification you don't truly notice till they're side by side. The piping home and away I can take or leave, leaning pretty well toward leave, because I appreciate how immaculate the A's, Dodgers, and Cardinals look in their home whites, but the addition is no dealbreaker, and piping on the colored jerseys is of course very much in play. I'm not sure about the standalone white elephant as a primary. I can't shake the feeling that it needs a roundel with "Oakland Athletics" in it. Being rooted in Oakland does seem to call for combining team iconography with the name of the city. Maybe I'm just used to the roundel the A's have used for so long, well before the trend.
But I'd say overall you did a great job fine-tuning a well-established baseball identity into something even better.