|My General Impression:
Hello! I had a lot of fun reading this. The idea really caught my attention. When I saw the title, I thought to myself - "Secret? What kind of secret?" Although your writing needs a little polishing, I still enjoyed myself. I even chuckled!
Reading from the perspective of the main character was interesting. He clearly has a lot of spunk and personality. I feel that you could have described the mysterious neighbor a bit more. At the end of the story, I felt confused. I still wasn't sure what the big secret really was all about. Did you mean to leave the finale in such a state of ambiguity? If so, I apologize. If not, you might want to consider expanding the last portion of the story a little bit. Some explanation could help the reader understand the situation better. This would make for a much more effective ending.
My review is going to cover a lot of things that made me stumble as I was reading. I think that the main aspect you need to work on is flow. You have a lot of points where you start and stop abruptly. You also have several commas that you don't need. I'm going to highlight those commas in red. Here are some examples:
"I raised my head(,) and looked through the open door(,) to see my neighbor’s yard. A lush green carpet. Mocking me. I giggled. I knew his secret."
Here, I would definitely consider expanding or combining some sentences. Short sentences with 2-4 words are a very effective way of catching attention, but if you use them too often they will make the reader's mind stutter as he/she goes down the page. You also don't need those commas. I recently received some great advice from a fellow reviewer. He mentioned that commas break flow and exist mostly for dividing thoughts in sentences. They should be used sparingly to avoid interruptions as we read. Below is an example of how I would combine these sentences:
"I raised my head and looked through the open door to see my neighbor’s yard. A lush, green carpet basked in warm sunlight, mocking me with its perfection. I giggled, for I knew his secret."
Another thing that caught my eye was your shift in tense. The majority of the story is told in past tense, but at one point it felt like you switched to present tense. Here is what I'm talking about:
"Each blade of grass is the same length (I measured one hundred and fifty areas across his lawn last year while he was gone on vacation). No ugly splotches of yellow dandelions dot his yard. No unsightly crab grass to ruin the verdant expanse. The edges of his lawn are perfectly trimmed. The mulch stays a rich deep brown, which somehow remains where it is placed. No brown smudges mar the green surface."
I absolutely adored the imagery in this paragraph. Aside from a few flow issues that I mentioned before, the only thing wrong with this was your use of present tense. In the next paragraph, you immediately jump back to past tense again. I've marked the present tense verbs in red. This isn't the only paragraph that does this.You should definitely consider revising.
"Swarms of fireflies danced in the night. Everywhere they flew golden dust sparkled in the starlight. What?"
Again, this is great imagery, but that "what?" at the end completely threw me off balance. I'm not sure it's really appropriate here. Maybe something like this would be smoother:
"Swarms of fireflies danced in the night. Golden dust sparkled in the starlight, illuminating their path. Needless to say, this wasn't what I expected."
Lastly, here is what threw me off about the ending:
"I lowered my head. Beth and the kids huddled off to the side of the driveway. How could I make them understand that I had discovered my neighbor’s secret? I started giggling. The ambulance door started to close. I struggled against the restraints.
“I know his secret,” I shouted.
My laughter echoed in the small space as they drove me away."
Where does the ambulance come from? Why was it there? What restraints are you talking about? Surely people don't get carried off to the hospital in the middle of the night because they're giggling . I would advise expanding this part a lot. Add more detail about the arrival of the ambulance and why someone may have called for one. Explain who is "they" in the last sentence.
Great imagery! There are many things for you to work on, but don't get discouraged. Everyone has different styles of writing. I can definitely see that you have your own way with words. You just need a little bit of direction and editing. I'm a newbie on the site as well. If this review was helpful, drop me a line and I would love to help you with other things you write. Best of luck!