It's not as good as iPhone's screen, but better than most other smartphones. It's a bigger screen though, if that's more important than resolution. (4.3" compared to 3.5") This does highlight the lower resolution though. (960 x 540 compared to iPhone's 960 x 640) The screen should still look fantastic.
Every other spec except storage outdoes iPhone 4, although I'd expect an announcement from Apple soon on a new iPhone, if that's what you're looking for...
I would say the biggest thing to look for is Android vs. iOS, Windows Phone 7, or Symbian 3, and choose whichever suits you best, rather than the physical specs.

The Iphone doesn't have a HD screen, the reason why it looks clearer or sharper is the pixels are closer to each other.

The Galaxy S II will be duel core and bigger screen 4.3inch but this screen will be amoled II which has the pixels closer and brighter screen.

The larger screen is much much better for typing on.

A Galaxy S makes an Iphone 4 look tiny, let alone the 4.3 and larger phones.

A big plus for me on the Android phones is the flash support within the web browser.