Nice build! Not sure what all the Reddit people are gushing over—you used pretty standard construction techniques and materials. Mine’s identical (only 12x6) and only took a couple of weekends too. I had never built anything like that before trying it. Basic wood construction is not hard at all. You just need to measure well and cut straight and take your time. For tools all you really need is a quality circular saw and framing hammer.
There's a lot of really shitty construction projects posted to /r/diy. It's a popular past-time there to point out all the things that were done wrong based on the submitted photos. There's been entire posts (usually of decks and the like) where the consensus is "That thing is so unsafe it needs to be torn down and started over from scratch." We're talking such fundamental inadequacies as not building a foundation, or not consulting load charts to determine spacing or lumber size. To give you an idea of how bad it was, I used taller floor joists, on shorter spacing, and with less than half the span, of some of the worst deck construction projects posted on there. Here's one example; unfortunately the photos have rotted away: https://www.reddit.com/r/DIY/comments/1da2rg/i_finally_built...
If you simply do the research and follow it, which is will within the capabilities of almost everyone posting here, then you should be OK. The mistakes you'll make will be relatively minor.
