Much better experience, fast deploys/builds. I miss Resharper but can live without it.
I don't know about OS X, but I used Xamarin Studio on Windows and it was horrible.
It feels much better on mac I must say, also tried it on Windows but just weird and slow.
I'm quite happy with it, but maybe I'm biased a bit because it sucked big time and they made big improvements to it last year. It's all relative ;-).
They've been denying it's a problem for over a year, and then acknowledged it a few months ago and did nothing about it.
The platform itself also harbors a lot of bizarre and difficult bugs that only cause a couple of crashes each under some very specific conditions that are nearly impossible repro consistently. But there are so many of them that on a given day, 5% of our apps will crash or freeze because of some Garbage Collector bug, a platform bug, or some platform race condition. Just check how many of the bugzilla bugs are still in the NEW state.
For me Xamarin Native was slow and rigid. I highly doubt I could make 'innovative' apps with Xamarin. Maybe it is okay for people who want simple things like a "to-do app" or somethign that fetches list of images and displays it.
I wanted more and found no solution for things I needed, so I gave up and started xcode (swift + some objective c).
And let me be clear here, if I had spent same amonut of time on xcode as xamarin I would have been iOS dev master :)
Things just works much better. You can do anything you imagine with Xcode and swift. With Xamarin its more like find whatever library is out there and try to create something by combining these. Too many bugs.
This is no sly dig on Xamarin or Microsoft as I use alot of MS products myself. I have also tried phonegap, react native etc. and Xamarin is the best when it comes to cross platform without a question, but none of these can match true native coding (xcode swift/objc)