If you've used Rush or Premiere Pro, you will find yourself relearning some things and - possibly - becoming frustrated at times because of those differences/limitations, but remember, this is beta software, with a very specific - and large - audience in mind; an audience of non-video professionals. And even now, in beta, I think this tool can help them in their storytelling goals.
I am pleasantly surprised at how good the final version from Express turned out.
Now that Express is out of beta, it is my hope that some additional functionality will be coming soon, such as proper cross-fades, better audio controls for fading music and maybe even ducking audio.
Doubtless, there will be a point in Express when you hit a wall in video editing, and that's where tools like Premiere Pro could become an option. With the creative confidence you've built using Express, you would be more prepared and open to diving into a more professional tool.
Or you could just as easily say - nah, Express is good enough for my needs.
And that's OK.
The whole point is to find the right tool for you to tell your story. I've quickly created several simple video projects using Express and plan to do more. Will it replace Premiere Pro for me? Not likely, but each tool will have its place.
If you haven't tried the Express for video creation/editing, give it a whirl. It may surprise you - as it did me.