The LG Chocolate BL40 is a beautiful handset. It's an irrefutable fact. Its shape is unique, its colours striking and it's one of the few phones these days that gets more ooohs and aaahs than a certain other touchscreen device that's somewhat taken over the planet. In fact, there's every reason to buy one - until you turn it on.

The sad fact that what the new Chocolate represents is that LG mobile has got pretty much as far as it can until it moves on from the S-Class operating system that hampers its top devices. On the one hand, it feels unfair to focus the review of a phone on its software but, unfortunately for the BL40, it's so integral to your every day enjoyment of this device that you've got to know what you're getting yourself into before you make up your mind to buy one.

Those with an Arena or Viewty Smart who are happy with the platform might well dispute what we have to say on the matter but anyone thinking of switching from S60, Android or even iPhone might well be in for a shock.

The trouble is that the S-Class OS feels more like a showpiece than something designed with functionality at heart. It's colourful and amusing to play with for the first 5 minutes but pretty quickly you realise that the four shortcut facets of the spinning cube GUI are basically redundant.

Once you do get to the one screen that counts, the one with all the app icons, it's just too fiddly here. Either you have the phone in portrait position where the rows of icons move separately and make it harder to find the ones off screen that you're looking for, or you have the Chocolate in landscape and the icons aren't well enough designed to be obvious as to what each one does. It's a shame because otherwise the LG BL40 has everything going for it.

The greatest tragedy of S-Class is that there are no third party apps you can add to customise your experience. The browser does indeed work much better on the Chocolate's extra widescreen than it ever has and the dual/split screen mode is actually a touch of brilliance here from LG. But it's still a clunky piece of software compared to something like Opera Mini.

The only other good additions are the gesture control and cut, copy and paste which works as intuitively as you could want but it's a shame that all these good software advances sit on the back of something can't keep pace with the rest of the phone world.

So, that is the enormous caveat that comes with this phone and if it's something that grates, then you will always covet another handset and rue the day you signed your life away, but others will still be impressed every time you bring it out your pocket because it is a stunning phone.

OSes aside, LG seems to have learned every lesson from every mistake in all their other mobiles and put it all together in the masterpiece that is this fourth black label device. The shape of the thing is so wonderfully original. It's not taken a single lead from any other phone and has set a new standard for design – one of the first phones to do so since Apple got started.

The long slender shape is not only elegant but also incredibly ergonomic and functional. It's unbelievably refreshing to once again hold a phone to your ear that's also close enough to your mouth to pick up every word you say. Better still though, is that outstanding screen making it rather reminiscent of the Philips 21:9 TV.

As it goes it's not just 16:9, but an AMOLED with a excellent WVGA resolution. Films on the go are given a great cinematic feel and probably the only other complaint to make at all about the Chocolate is that it's a little too reflective outside in the sun. Come to think of it the fact that the accelerometer only works in one direction is rather silly too.

That aside, the black gloss finish is a real treat topped off perfectly by the smart scarlet ridges at the top and bottom ends of the phone. The few and well-chosen buttons and ports are superbly implemented with a shortcut to music, a shutter release, volume controls in the perfect finger position, an on/off/lock switch at the top, a universal Micro-USB for charging and data transfer complete with a tidy, sturdy and secure cover flap and, joy of joys, a 3.5mm jack too. Full house. We thoroughly approve.

Apart from the on/off switch, every function of the Chocolate can be controlled by the screen which supports an excellent level of multi-touch that's a breathtaking advance on previous efforts. If only there was a browser worth pinching at.

Phone connectivity and reliability is very good with the full complement of HSDPA, Wi-Fi and Bluetooth, and all the expected AV file types are supported in the familiar and user friendly LG media players.

The camera is typically strong with a healthy 5-megapixel sensor and Schneider-Kreuznach optics. It carries most of the features you'd expect on LG smartphones with plenty of exposure controls and recognition settings plus a decent LED flash. We are slightly disappointed by only VGA resolution video capture, which shows up quite badly on the phone's excellent WVGA 345 x 800 pixel screen. It would be nice to see the touch-to-shoot and other top end features packed into the Renoir but otherwise, all is well in this department.

On the practicalities side, the BL40 is a medium to heavy 129g but nothing like other lead weights you can buy and, although some may sneer at the unusual 128 x 51 x 10.9mm dimensions of this slim stunner, it's as good in your jeans as in a coat pocket. Mercifully the battery poses no problems either, even after a day of heavy use.