Nitro is not supposed to be feature rich.
It is supposed to be lean and mean. It's like a stripped down car. You remove all the creature comforts that add weight to the car so that you are left with the bare bones and a very light car. The result is a car that's fun to drive, because it goes like stink and handles well, but it has no radio, no carpets, no electric windows, no sound insulation, and so on. If you are the sort of person that would trade a bit of speed for some additional features, then that car is not for you.
I used to drive a Caterham as my everyday car. It's not for everyone, but it was wicked fast, it handled like a go-kart, it was very noisy, it had no creature comforts whatsoever (apart from seats), and every time you got inside you hoped it would not rain. Not for everyone, but it was a blast!
From my own testing, by using Nitro every day as my default browser for over a week now, I think it really is fast. And yes, I do go back to other browsers (Chrome, Firefox) to compare, so it's not just psychological. By the way, the HTML5 test (which some people have mentioned) is not about speed, it's about coverage of HTML5 features. Maybe there is some speed hammering benchmark test says it doesn't have the highest score (is there?), but overall speed is more than just hammering one aspect. The biggest impact for me is the perceived loading time for a new page, which is really fast.
Personally I also like the simplicity of it. Less is more. Long ago, I used to use Outlook for email, and then I moved to Gmail. Hands down Outlook has tons more functionality, but Gmail is refreshingly simple and I can do everything I need with very little mental effort (and it gives me access from all internet devices, but that's not my comparison here). There's no going back to Outlook for me.
So Nitro is supposed to be lean and mean, and refreshingly simple. That's that whole idea. If it's not for you, then that's fine and you have other choices. It is for me.
I think there are some pieces are functionality that could be added without compromising the vision of Nitro. UI commands can be added to context menus for example. This should not interfere with speed or visual simplicity.
I love the mouse gestures by the way, which is something I used all the time with Chrome (Smooth Gestures extension), and it's nice to see that the same gestures do the same thing. Mouse gestures are just a way to execute a UI command, so these should not affect performance. Someone commented that they might be taken away at some point. I hope not. By the way, where are they all documented?
Ad blocking (something that people keep mentioning) is an algorithm that runs while the page is being loaded and rendered, and this could well slow things down, even though the resulting rendered page is simplified. There is an argument that ad blocking reduces the amount of data that needs to be downloaded, which should improve speed, but it also introduces processing delays into an algorithm that would otherwise just request everything in parallel. I imagine another objection to providing ad blocking is that this would call for a add-in framework, and then if you open this up you've opened the door for slowing things down and you are back where you started with a bloated slow browser.
My enhancement list would be:
History. According to the tool tip, right-clicking on the Back button should show navigation history, but it does nothing.
Keyboard shortcuts. Even the standard ones are missing: prev/next tab, close tab, back/forward, etc.
Context menu commands for 'close other tabs' and 'close tabs to the right'.
Support for multiple windows and for dragging tabs off into a new window, or between windows.