CNET editors pick the products and services we write about. When you buy through our links, we may get a commission.
The NX series is Sony's line-up of mid-range screens that sit between the entry-level Bravia EX models and the higher-end HX tellies.
The KDL-55NX723 is the largest of the NX TVs. It uses LED edge-lighting, boasts a good range of Internet features and offers 3D support.
It can be bought online for around £1,500.
Sony has given its old PS3-style menu system the heave-ho. In its place comes a new system that retains much of the feel of the old one, but tweaks several aspects of it.
For example, when you call up the main menu, it no longer takes over the whole screen. Instead it shuffles the selected programme or video feed into a large window on the top-left of the display, which is less obtrusive.
Below the video window is a row of icons that you can shuffle left or right to select features. When you choose one of the icons, a vertical sub-menu on the right-hand side of the screen populates with further options; if you select the Favourites icon, you can then vertically scroll through a list of the stored channels.
This system takes some getting used to. Although it's faster than the old approach, it's still not as immediate as the more straightforward and attractive-looking menus found on the latest Samsung and LG sets.
Thankfully you don't always have to resort to the main menu when you just want to tweak picture or audio settings. Instead you just call up a mini menu that offers quick access to these settings by pressing the Option button on the remote.
The picture controls are comprehensive, allowing you to tweak the usual colour, contrast and brightness options. They also give you control over colour hue, gamma and temperature, although there isn't a full colour management system. Nevertheless, you can play around with some of the extra processing features including the Black Corrector, Contrast Enhancer and Skin Naturalizer.
The set's electronic programme guide (EPG) is a tad drab but the traditional horizontal layout works well. Programming information is neatly laid out and easy to read. It shows eight channels' worth of data at a time but only two shows per channel. It's smooth to scroll back and forth through programmes so this isn't a problem.
This set makes the most of the fact that it has both Wi-Fi and Ethernet onboard by delivering a very impressive line-up of Internet video services.
As you would expect, BBC iPlayer is included, but alongside this you'll find a wealth of other services such as Demand 5, Sky News, LoveFilm and Sony's own Video Unlimited (renamed from the old Qriocity moniker) movie rental offering. In terms of available video content, it's probably the best offered on any TV at the moment.
The range of available apps isn't quite as impressive. There are widgets for Facebook and Twitter that show feeds from these social networking sites in a box while you're watching TV. In the Bravia Internet Video menu you'll find a few more apps for sites like Picasa. However, the options are limited overall. While it does have a full Internet browser, it lacks Adobe Flash support, which means it can't display video from some websites.
Like a lot of Sony's previous TVs, when it comes to media playback, this model is hit and miss. On the one hand, it'll happily play a range of file formats like JPEG pictures, MP3 music tracks and Xvid and DviX files; it can do this either locally from its USB ports or by streaming them across your home network from a PC or NAS drive. However, it doesn't work with MKV files -- a format that's steadily gaining in popularity on the Internet and which is now supported on most other manufacturers' TVs.
The KDL-55NX723 follows the Monolith design that we've seen on other Sony TVs such as the KDL-40NX713. It looks gorgeous. Not only is it amazingly slim at just 27mm deep, but it's also got a really stylish single-sheet-of-glass look; the glass on the front covers both the bezel and the surface of the screen, blending the two seamlessly together. We're also fans of this model's thin and sleek pedestal stand, in part because of its slick brushed metal look.
Unfortunately the remote hasn't received the same level of tender loving care. It's essentially a long and thin slab of cheap-looking plastic that's at odds with the premium feel of the telly. Its squared edges mean that it's not as comfortable to hold as it should be. On the plus side, the placement of the various buttons is sensible, so all the TV's key features are within easy reach.
This model has a Freeview HD tuner onboard, but lacks the Freesat HD tuner that you'll find on some higher-end models from the likes of Panasonic and Samsung.
The slim chassis means that there's not enough space for full-sized Scart and component connectors so Sony supplies break-out cables in the box. As you would expect, this model also has four HDMI connections. Two of these are mounted on the rear, while the other two have been placed on a panel on the right-hand edge of the TV.
Thankfully, Sony has sensibly decided to build Wi-Fi into this set, but there's an Ethernet port in case you want to use a wired connection instead (it often provides more reliable streaming for HD video files). There are also two USB ports, which can be used for digital media playback.
When it comes to audio, this model is something of a let-down. The speakers are reasonably loud -- certainly loud enough to fill a decent-sized front room -- but the audio they produce is hollow and gutless. The main reason for this is a lack of bass that leaves it sounding thin and lifeless.
Sony seems to be aware of this issue as it offers an alternative stand, the SU-40NX1, which bumps up this model's audio as it includes 2.1 speakers. It looks great as it tilts the TV back at an angle of 6 degrees. However, this is a pricey addition at £200. When you combine that into the overall price, you could get a higher-end model from many of Sony's competitors.
The KDL-55NX723 is a strong performer when it comes to 2D pictures. It does a great job of upscaling and deinterlacing standard-definition pictures, helping them to look that bit sharper and more defined, without introducing a glassy, processed look. High-definition video looks stunning thanks to this model's sharpness levels.
The screen manages to produce a bold, yet natural-looking colour palette. But its black levels and shadow detail that are most impressive; this model produces really deep and dark blacks, while also teasing out plenty of finer detail in darker areas of the picture. You can still see some backlight inconsistencies on this model -- something that affects almost all edge-lit displays -- but they're less noticeable than on a lot of rival manufacturers' sets.
However, our model did have a thin strip down the left-hand side, just next to the bezel, that seemed to be lit slightly differently to the rest of the display. It shows up as mildly brighter or darker than the rest of the picture. The effect is only noticeable when showing uniform blocks of colour and it's very close to the edge of the screen, but it is there nonetheless.
Unfortunately no 3D glasses are supplied with this set as standard. You'll have to factor the extra cost of these into the equation if you're planning on using it for 3D viewing. The glasses are priced at around £80 each, which is expensive. Worse still, they're not that comfortable to wear. They feel much heavier than Samsung's active specs, for example, and have a tendency to suffer from flickering when there's ambient light next to the TV.
Previous Sony sets weren't hugely impressive when it came to 3D, often displaying a lot of cross-talk -- where you can see images ghosting on the edges of objects in the near and far distance. This set is better in this regard as mid-distance objects look more solid. However, background objects still suffer from a fair amount of ghosting.
It's a long way off the solid nature of Panasonic's TX-L37DT30B. But the 3D pictures are still very watchable and the glasses don't dim the image as much as some active specs that we've used. That said, you'll definitely get better 3D performance elsewhere.
We love the KDL-55NX723's bold design. Its 2D picture performance is very impressive, thanks to its ability to deliver bold colours and deep black levels.
However, for a set that costs a grand and a half, it puts in a comparatively poor showing when it comes to 3D pictures and audio performance.