WHY are you doing it, besides believing it would be a nifty technique? How does it make the story BETTER for the reader?
Reading is not a one-way street. Readers will fill in blanks, based on their own preferences and assumptions. So, if you don't give the reader any kind of image to go with the character (and a name and gender is at least something to start with), and assuming the reader doesn't toss the book aside in frustration/boredom, because you're making the reader create the story instead of creating it for the reader, then the reader's going to fill in the blanks. What's that reader going to do when, in chapter 7, it's revealed that this Amazon-sized female character the reader's been imagining and really bonding with is actually a puny little male? Throwing the book against the wall is the least negative of the likely reactions. Staking the book through its heart and then burning it -- and author's effigy and reputation by way of reviews -- is an equally likely reaction.
It's one thing to be vague about the details, to let the reader fill in the eye color and hair color, but to intentionally withhold the name and gender and some visual cue, is very, very, very seldom going to benefit the reading experience. It's fine to say that what's inside matters, but the fact is, we need something external too.
As an aside, if this is written in first person, the conventional wisdom is that a reader will absorb that like a role-playing adventure, putting herself into the "I." Personally, I doubt it. It's certainly not the way I absorb first person. If anything, the "I" pronoun is a constant reminder that the character/narrator is NOT me. In real life, we're used to hearing people say "I" when they're talking to us; that "I" is NOT me, and I know it. That "I" used by someone else is still "other." To the extent I'm going to conflate my own experiences with those of a narrator, it's more likely to happen with "she," because in real life, other people (authors) are talking about me, they're using "she." I'm much more likely to identify with "she" (or even "he") than with an "I" that's spoken/written by someone else.
On top of that, it's not entirely clear that readers insert themselves into the action. It's equally likely that readers are viewing the main character as their best friend, rather than as themselves. There's a lot of stuff we read about that we enjoy experiencing second-hand, but wouldn't really want to be experiencing it first-hand.