It's been out for less than 24 hours and it's clear that Drafts 4 is going to be a huge success. The online reviews are amazing and the time and effort that developer Greg Pierce has put into this paid for upgrade is clearly visible to the end user.
I love the new top line to the keyboard which allows me to scroll through to my Markdown shortcuts. Heck, I love the fact I have Markdown shortcuts! Writing emails in Markdown on my iOS devices is going to be a dream.
It's optimised superbly for the iPhone 6 and there is a lot of real estate for your to construct your drafts however this isn't at the expense of detail, which was a complaint with Drafts 3. There, the background seemed a tad sparse however there are more on-screen options here with Drafts 4 and it looks fantastic.
I've only just started getting to grips with it and adding both my own actions and downloading them from the Action Directory (which is already filling up quite nicely) so for a detailed analysis I strongly recommend you visit Federico Viticci's review on MacStories for a top notch review