Bleeding Cool has said about the series,
"if you're a fan of anyone involved or fantasy fiction that's red in tooth and claw, this is absolutely for you. Just stunningly good work, in every way."
"This is a book that fantasy readers want. The artwork is exceptional. The colors are seeringly interesting. The pacing is unpacked and gives the reader time to react and take in the dreamy, strange vistas of the book. There's even the fact that the lettering is unassuming and kind of understated that contributes to the overall charm. There are maps, strange names, plenty of swearing, and a kingdom that thinks it's conquered a very dark past only to find it rising up again in tandem with an eclipse and a magic object."
"Cheerfully horrible, and just flat out cheerful in places. Umbral is tremendous fun."
"One of Johnston's greatest talents is to write real people. There's no convenient plot servicing here, just people reacting like normal, real, non two-dimensional fictional people do. I love that Rascal puts together a completely plausible reason why Shayim can't possibly be who she says she is. I love that she acts on that. Most of all, I love that she's wrong. No easy answers in this book, not for anyone."
"Worldbuilders of the highest order, the Johnston/Mitten duo bring that rare kind of brilliant collaborative lightening that creates unique and vibrant universes wherever it strikes. Umbral is no exception."
Sadly, there weren't enough people who seemed to share those opinions. Writer of Umbral, Antony Johnston posted on his Tumblr,
With great sadness, we must announce that UMBRAL is going on hiatus.
This isn't a creative decision. We all love making UMBRAL, and we know there's a small, loyal audience out there who love reading it. You're our kind of people, and we love you all.
But the operative word there is "small". UMBRAL no longer has enough monthly readers to continue — in fact, it hasn't for some months, now. We persevered, hoping things might turn around, but they haven't. (Before you ask about trade paperback sales; they're respectable, but not enough to make up for the monthly shortfall.)
Some critics have suggested UMBRAL would have sold better if Rascal was a boy, or even a sexy adult woman, instead of a young girl. I sincerely believe that's not true, but even if it is, I speak for the whole team when I say: f— that noise. We won't play that game.
So. Hiatus? Yes, truly. If there's a way we can somehow return to continue Rascal's story, we promise that we will. There's so much you still haven't seen! Her second encounter with Black Rojyr, on the high Azqari Sea; how she discovered the lost capital of Xulinor, and the secrets she found buried within; the Mistwalker's long path to freedom and reconciliation; the tragedy of Dalone's true history, and what really happened at Culin's Calamity; and more, and more, and more.
For now, those stories must remain untold.
For now, we say au revoir (never goodbye) to Rascal and Dalone, Shayim and Munty, the Oculus, the Mistwalker, and of course, the bastard Umbral themselves.
For now, we retreat into the shadows.
— Antony, Chris, Jordan, Thomas