As a writer, I am intrigued by writing in the first person. It’s fun because it’s personal—to the character—and more “conversational”. The protagonist’s thoughts and experiences are unique to his/her personal point of view. However, there are some caveats.
First of all, the reader is immediately let in on the fact that the first-person character has survived whatever is about to happen in order to tell the story. Doesn’t work if you protag is rubbed out in chapter 19.
Readers can only know what the character knows, can only experience what s/he experiences along the way. This can make it a challenge for the author to convey important information to the reader without relying on hackneyed memory flashbacks or info-dumping conversations with other characters. The reader also might find it difficult to “see” the character’s expressions, get the full impact of his body language unless the writer is adept at describing them without sounding forced.
“I grimaced at myself in the mirror.” “I felt my eyebrows come together in a decided, confused frown.” Hmm.
On the plus side, first-person is easier to control, especially if the writer has difficulty in third-person with regard to head-hopping through multiple point-of-view characters. There is no choice here. Additionally, readers often find it easier to identify and sympathize with a character when they spend the whole book inside that character’s head. There’s an intimacy created with the protagonist that cannot exist with other characters.
Many mysteries are written in first-person for these very reasons. However, in cases where the character in question does not survive to tell the tale, or where the reader needs to be allowed to “pull back” a bit from the character in order to “see” more of the story’s surroundings, a limited third-person point of view may be more beneficial. Some mystery authors prefer this technique, because although the POV is limited to one character, the writer has more freedom with regard to what the reader is allowed to experience.
In my romantic novella STARFIRE, my protagonist is an attractive, lonely accountant who happens upon a chance to have a fling with a well-known actor. Because the reader is treated only to her fears, her desires, her angst, I can control the reader's sympathies toward her, despite the fact that others (her husband, her children, etc.) could have very conflicting views of her behavior.
The choice is yours. But if you’ve never written (or read) a first-person story, I recommend you give it a try, if for only a short. For authors, there is a discipline to staying on that first-person path that will benefit third-person or limited-third-person writings of future work. For readers, it’s just great fun to “become” someone else for the next 300 pages, solving the mystery one step at a time with the protagonist.