Doors into Prayer is not a book I would have picked up on my own. It is well worth reading, but I would not have picked it up except that it was part of the Renovaré Book Club. (The next book is Interior Castles.)
I do not participate much in the online discussion, and I do not attend a local in-person discussion (although those are available for interested people). But I do read the supplementary articles and listen to the podcasts. Most of that is paywalled and only for those that participate in the group, but this is a free talk that Emilie Griffin gave at a Renovare conference that is worth listening to (Dallas Willard joins her for some Q&A at the end).
In a paywalled podcast, Griffin says that she wanted to write a book on prayer that was good for standing in line or other short reads. Something that can be read in a few minutes and not tightly connected to the material around it. And that is what this is.
I think of it kind of like those readers digest humor stories. Most topics (chapters) are less than two pages. And while I often read two or three at a sitting, I rarely wanted to read more than that. These are things you want to read and then step away and think and/or pray about.
I am not a fan of books on prayer that are not oriented toward helping us actually pray. We learn to pray by praying. It is not that theology of prayer or practical help style books are not helpful, but that it is easier to read about prayer than do it. In general, I try not to pick up books about prayer unless I am ready to try to put it into practice right away.
There is not a lot here that is unique, but there is a lot of accumulated wisdom that I think is helpful to have collected together. If you are looking for a book to read standing in line, or as a morning thought before you go on your way, or something to read right before bed, this is worth reading.