The particular version of Android on show here is Android 2.3.3 Gingerbread, which isn't quite the latest (2.3.4 adds video chat) but the Galaxy S2 suffers little because of this, and an update should come relatively soon. As usual, Samsung couldn't resist giving the interface a bit of a visual tweak.
The most obvious change is that the main desktop/homescreen (the one the home button takes you to) is the left most one (as opposed to the middle one) with six others available off to the right and none to the left. If you swipe as though to access a screen to the left of the homescreen, it just bounces off rather than looping through to the right-most one as you'd expect.
This is downright annoying as it means you can only access one other screen within one swipe of your finger, whereas if you're free to swipe to the left and right you can access two pages within one swipe. It may sound very picky, and indeed if you tap the tiny dots that run along the bottom of the screen you can access all the homescreens in one motion, but it's just such a silly little usability failure. And one can't help but think Samsung has done it simply to make the phone look/feel more like an iPhone, without thinking about the usability.
Another annoyance is the lock screen. Once you've activated the screen with the touch of the central home button or side power button you can unlock the phone by swiping the picture in whatever direction you want. Great! Except because there's no visual indicator to tell you how far you need to swipe, it can take several goes for it to successfully register that you're trying to unlock the screen, otherwise the picture simply snaps back into position.
From here on in, though, this phone is a breeze to navigate, and has a particularly good homescreen manager. Just as with other Android handsets, you can simply drag apps to and from the various homescreens or add folders of apps and widgets to them. However, Samsung has upped the usability by splitting the screen and having the homescreens presented as shrunken versions of themselves in a carousel arrangement at the top, making it easier to see where you want to place things. You can also resize widgets using a simple grab-the-corner-and-drag method. You can't start an app folder by simply dragging one app on top of another though, as on the iPhone and Sony Ericsson's latest Android phones.
This same visual style is also used to let you rearrange the apps in the main menu (App Launcher). While this customisation is welcome, it's rather annoying that you can't simply choose to have all your apps in alphabetical order, as most Android users have become used to. After all, with all those homescreens as well, having to organise the main menu just means you have two things to keep on top of.
Also of debatable benefit is the addition of 'tilt to zoom'. By holding two fingers on screen and tilting the phone back and forth you can zoom in an out of the usual selection of apps such as the picture viewer and web browser. If ever there was a feature to represent the word 'gimmick' in the OED, this could well be it. Thankfully you're under no obligation to use it.