The Samsung Galaxy S (or GT-I9000) was shown off last night at a star-studded launch party in London and we were on hand to have a play with the new handset. It is already on pre-order and some of you will probably receive your Galaxy S before we get our hands on a review model for a prolonged test, but we thought it only fair to give our first impressions.

The first thing that hits you about the Galaxy S is the size of the screen: 4 inches puts it out there with the biggest phones around. It has one of Samsung's Super AMOLED displays, like we saw on the Samsung Wave we've just reviewed. The resolution is the same as the Wave at 800 x 480, the current top (ish) definition on phone screens until the iPhone 4 lands next week.

At first glance the Galaxy S display didn't seem to be quite as striking as the Wave - a lower pixel density may be the cause - but it's too early to really judge the screen without living with it for much longer. Whilst on the screen, we watched some 720p movie trailers on the phone, and at this size, it should make a very popular portable device for watching video back, especially considering Samsung's attention to codecs we've seen in the past - something to check in a full review.

The handset measures 122.4 x 64.2 x 9.9mm, so despite the large screen, it isn't overly fat (it shaves 3mm off the size of the Sony Ericsson Xperia X10). It feels light in the hand considering the size at 118g.

The construction is mainly plastic, so you don't get the sort of luscious metal body that you'd find on the HTC Desire. It has a glossy finish to it too and it was immediately obvious that you'll spend regular periods wiping the fingerprints off. Whilst we had it we found the screen easy enough to wipe down, which is the most important part.

We've become accustomed to finding four control keys on Android devices, mostly because of HTC's dominance. The Galaxy S has three, which are Home, Menu and Back, the former being the central hard button, the latter two being touch.  Around the sides of the device you'll find a volume rocker and power/lock key, but strangely no dedicated camera button.

There is both a forward facing camera and a rear-mounted 5-megapixel camera. Although some people are starting to make noises about 8-megapixel cameras, we don't think that increasing the pixels on the tiny sensor is any great benefit. We had a play with the camera and found familiar camera controls with a range of scene options and so on, as found on other Samsung handsets. There is no camera flash.

The rear camera also gives you the option of capturing 720p video, which is a welcomed addition for those who want to take advantage of YouTube HD, and we'll be sure to give this - and any related editing and sharing options - a thorough testing when we have a handset in for a full review.

The Samsung Galaxy S runs Android  v2.1, with Samsung telling us that there would be an OTA upgrade to v2.2 before the end of the year, but didn't give us a definite timeframe. It's great to see v2.1 of Android on this handset considering that there are still v1.6 devices launching and on the market (the Sony Ericsson Xperia X10 is an obvious example, although it announced a v2.1 upgrade in Q3 today).

Whilst we were playing with the Galaxy S, however, its Android credentials remain somewhat hidden because of the overlay of Samsung's TouchWiz 3.0 interface. A Samsung spokesperson told us that you would be able to disable TouchWiz and run the Galaxy S as a relatively vanilla Android device, but we didn't try this during our hands-on session.

TouchWiz 3.0 gives you the same sort of deep integration that HTC Sense does and offers some of the same sort of features. After getting your Google accounts set up, you also have the option of connecting up with other social networks: Facebook, Twitter and MySpace, with the option to "get friends" to populate your Contacts, just as we saw in the Samsung Wave.

You also get the side-swiping homescreens where you can drop widgets, with a selection of Samsung and Android widgets. This gives you a great deal of freedom, and you can also drop shortcuts and bookmarks across these pages (we saw 7 pages) so you can possibly do away with the need to access the menu too much.

The menus have also been redesigned, so you get a side-scrolling arrangement rather like the iPhone, something we actually like quite a lot, and we were impressed with the level of detail on offer here, as Samsung have also customised the application icons - it will be interesting to see how it deals with all those extra apps you'll be adding.

When it comes to applications there will be a selection pre-installed, but mostly Samsung apps. We questioned some of the Samsung demo guys on applications and they confirmed that Samsung would be developing its own apps and widgets in addition to the regular Android apps, so you get both the Android Market and Samsung Apps in the menu.

We spotted Layar and the Aldiko ebook reader app pre-installed (which we saw on the Archos 7 Home Tablet), as well as a collection of Samsung applications: AllShare, Daily Briefing and Social Hub. AllShare lets you stream media via DLNA which is pretty exciting, although we'll have to test it to see exactly what your options are here.

Social Hub offers up a combined message management tool, but on the Bada platform this merely linked you through to the respective application, so it will be interesting to see how this works on Android. Daily Briefing is a sort of weather, shares and news feed.

We didn't detect any sign of lag as we explored the Galaxy S and with a 1GHz processor at its core, we wouldn't expect to find any if the TouchWiz interface has been thoroughly optimised. It's too early to tell, however, so we'll be reserving any judgement on response and the keyboards (including the integration of Swype) until we have longer to play with the phone and get the chance to fill it with content.