LG's theme for the G3 is 'Smart is the new Simple' and one of the key factors in this is the all-new interface it's put together for the new handset.

One of my big criticisms of the LG G2 was that the interface was simply awful: cartoon-like, hard to understand, cluttered and simply not up to the standard the HTC One M8 and friends offer.

So it's great to see that the brand has gone back to the drawing board and made something that's more fitting with a top-end handset. The garish colours are replaced with more muted 'mature' hues, meaning out goes the bright yellow and purple to be replaced with softer greens and autumnal burnt reds.

LG G3 review
The interface is much less cluttered compared to the G2 (centre)

Each core app, such as contacts and messaging, has its own colour to help you discern where you are in the phone – if that was a confusing problem for you – and the notifications bar has been stripped right back to simply pack a row of quick settings and the stuff you want to know about.

By default you do have a brightness bar and the option to control volumes (which is useful when you're using the phone in landscape) but these can be toggled on or off, depending on your preference, which allows for a very clean notifications zone.

If you think of it as somewhere between Samsung's new TouchWiz and native Android 4.4, you'll be pretty close. It's not as close to standard Android as some would have you believe, as the notifications area and menu systems are different, but the ethos is there and it's very similar.

The interface is visually a triumph for LG, a new look that brings a freshness that sends a statement that the South Korean brand is finally looking to make the step up to top-tier manufacturer.

To that end, there have been a couple of extra features added in to help with day to day living – these include helpful video tips that alter throughout the lifetime of the phone (so start-up tips in the first few weeks, app tutorials for the programs you're not using a bit later on and then telling you about new LG products as the G3 nears the end of life).

LG G3 review
Smart notice can be a bit foolish at times... 'friend's birthday'

The idea is clever, but one you'll not really use that often. The same can be said of Smart Notice, a constant label that hangs beneath the weather widget on the home screen.

This is meant to be the companion in your phone, allowing you to see the truth behind the weather by prompting you when you'll need an umbrella or offering to save a contact that you call multiple times but isn't in your phone book.

The thing is more often it tells you when there's a new video to watch, or adding helpfully that when it's foggy outside 'it's very foggy'. The idea is cool, but it's more annoying than helpful, at least in the first month of ownership.

I also got a number of shipping forecast-style updates when in New York. Helpful.

So, onto the performance of the LG G3; as you can guess with the Snapdragon 801 CPU on board and up to 3GB of RAM (if you buy the 32GB iteration of the phone) this handset performs well on standard benchmarks.

However, in day to day use it's not great. There's a definite lag under the finger that's simply not present when using the HTC One M8 or iPhone 5S, and it's quickly noticeable.

In side by side tests opening and closing apps was markedly slower on the LG G3, and while we're talking nanosecond differences it does all add up. I definitely felt the G3 wasn't as slick as other handsets on trial, and the problem didn't resolve itself between getting the European version of the software and the pre-production Korean handset.

It's not deal-breaking, but I'm confused as to why a firm that prides itself so much on engineering would let something like this slip through. There were also few freezes here and there, but nothing that you won't see on most other smartphones.

The benchmark GeekBench 3 results could give a clue as to why - the LG G3 doesn't perform as well as the rest of the competition, which could be partly down to the extra pixels needing to be driven. It's surprising, given LG usually bosses these tests, but Geekbench is designed to replicate real life use as much as possible, and the results tally with the way I found using the phone.

LG G3 review
While it's not as extreme as the graph looks, there is something of a lag on show

App compatibility is still an issue as well: some of the top apps simply aren't there, such as Real Racing 3, making it hard to properly test some elements of the phone. These will probably come in time, but be warned that if you're using the LG G3 from launch you won't be overly happy with some of the limitations.

Knock On / Knock Code

LG's proprietary way of unlocking the phone is back for a second round – and it's as good as it was before.

The notion is simple: you tap the screen twice when turned off to unlock the phone (if you've not got lockscreen security set up) and can then tap the notification bar twice in quick succession, or any empty area on the home screen, to shut it down again.

It worked really well on the LG G2 to the point where, like the rear buttons, I often tried the same trick on other handsets. Others are coming on board now, like the Sony Xperia Z2 or the HTC One M8, and of course it was Nokia's idea in the first place to invent the technique.

LG G3 review
Knock code works, but it's a bit clumsy at times

But none do it as well as LG, and it's a real boon.

And that's where the brand reached a little too far in my opinion by adding in Knock Code. It's a clever system where you can simply tap the right quadrants of the screen with the screen turned off and it works the same as an unlock code or pattern.

The issue I had was that it didn't register 80% of the time. This was often down to the fact you pick the phone up holding a portion of the screen, which seems to register as an early tap to add into the code.

This means the screen still lights up, but prompts you once again to enter the code. If you must have security then it's OK, but tapping the display twice to wake it and entering the pattern is a little simpler.

That said, if you opt for the simplest pattern first and really try at it, you'll get some joy more often than not, and when it works Knock Code is second only to the iPhone's TouchID in terms of a simple way to open the phone.