I've been suggesting other Golden Age detectives lately on Twitter; but not because I dislike Arthur Conan Doyle. Some readers may, like me, find that ACD isn't enough for a year or more.
I'm quite fond of GAD mysteries. :)
Ellery Queen was several things. The pseudonym of a writing team, two cousins, who I tend to call the Queen cousins. A gentleman detective who writes detective novels. A detective character in novels. And, not least, the name of a man whose true name we never know: Ellery Queen is not his name.
Plus the Ellery Queen Mystery Magazine still going strong. "And there's EQMM, bless its bloody heart" Ellery writes to Tony Boucher [paraphrased].
This is not counting the Ellery Queen house novels -- contracted out to ghostwriters, see Wikipedia -- nor the Barnaby Ross novels.
The Ellery Queen novels come in several flavors. Starting with real or original EQ, there's a full four incarnations of Ellery starring in these. Really.
1) The first nine novels [the Nationality Something Mystery set] are based on another detective. Ellery the First eventually stops being his near-clone as the series develops. I read The Roman Hat
2) The next set are considered the Hollywood years, from the novella The Lamp of God through The Dragon's Teeth. [Disregard the fact that another later novel's set in Hollywood by its copyright and just roll with it.]
3) Then we hit Wrightsville. The third incarnation of Ellery is quite pleasant and more social, still witty as all get out, and has met -----. This period ends in 1958 if you go with the Queen cousins' last official novel, The Finishing Stroke, or in 1953 with the final Wrightsville novel, The Scarlet Letters.
Note that The Finishing Stroke (which I adore) is written to seem like Ellery the First, but is written as Ellery III. If you happen to start with that book, early Ellery is not quite like that!
4) Last are the ghostwriting years of 1963-1971. (I've gotten into arguments about this, because I know their style so well; the fully ghostwritten novels can't imitate the cousins.) The Queen cousins wrote Inspector Queen's Own Case, but alas, not enough of A Study in Terror. :(
If you meet Ellery for the first time, I think you should read the short stories first. Develop a taste for Ellery's wit, and possibly for the puzzles, before essaying the novels. Starting in Ellery III territory is best.
Happy chase to you!