I was a tester for it recently against the iPhone.
Its not a bad little handset, but has its flaws.

Good things:
- GREAT screen
- Very Smooth
- Very Responsive
- Can have as many Widget/Menu screens as wanted
- Colours are brilliant
- Music Player is pretty decent
- Useful Widgets

Bad things:
- With a few Applications you can end up with 9-10 menu screens.....
- Feels very simple
- Camera is less than impressive
- Keyboard WAY too small
- Widgets are too big, resulting in 1-2 widgets per page

Those are some of the things that I think about the phone, I spent the day playing around with it and gauging what I thought. Its a decent phone, but it tries to carbon copy the iPhone in a lot of ways, the biggest problem for me is that the keyboard is tiny on screen and almost impossible to use. Other than that it probably has the best screen I've seen on a mobile phone to date!
Generally though, Bada doesn't feel/look any different to any of Samsungs other mobile phones, almost as if they just wanted their own OS to play with.....