The LG G3 is a tough act to follow, as it was one of the first phones with a QHD screen, as well as featuring an innovative camera with a super-fast laser autofocus.
To ensure that the LG G4 is a decent successor, LG had to do more than just match and upgrade those features, it also needed to impress us with some genuine innovation - and that's no small task.
Thankfully it's a challenge that the LG G4 has risen to, as it's taken many of the best bits from the LG G3, like its screen, and not only improved on them but added various new bells and whistles too.
So is the LG G4 an improvement in every conceivable way, or has it just got a shiny new coat of paint? We put the two phones head to head to find out.
The LG G4 looks distinctly different to the LG G3 and that can only be a good thing, given that we weren't huge fans of the G3's lightweight plastic chassis, and the metallic effect on the G3's shell looks nice but isn't entirely convincing in the hand.
The LG G4 replaces the G3's faux-metal with a vegetable-tanned leather back (similar to the Moto X), which looks and feels far more premium and combined with a gentle curve it's designed to provide a more comfortable grip.
The LG G4 is also available in two leather variants; brown and black, with the former looking more impressive, but the latter feeling more rugged (and also feels nicer to hold).
But if you were a fan of the G3's polycarbonate LG has also produced a plastic version of the G4, with the same metallic design as the G3 (as well as one with a ceramic look).
Unfortunately the leather is too thinly stretched over the back of the phone, which results in that version of the LG G4 not feeling as premium as it should.
As with the G3, the G4's polycarbonate body also feels slightly cheap, especially when pitted against other flagship handsets with metal bodies such as the HTC One M9.
Whichever option you go for LG promises that the G4 is 20% stronger than the G3, though it's also slightly larger and heavier, at 154g and 149.1 x 75.3 x 8.9mm.
The LG G3 on the other hand is 146.3 x 74.6 x 8.9mm and 149g; it's not a huge difference but then the G3 itself isn't a small phone, so the LG G4 definitely isn't the handset for fans of compact designs.
However while the LG G3 feels like it is just on the edge of being too big, the LG G4 has been curved to make it feel a little more comfortable to use with one hand.
There's less to choose between the screens, as both phones have a 5.5-inch 1440 x 2560 QHD display. But as a discerning phone buyer you know there's more to screens than size and pixels, as while the LG G3 has a True HD IPS+ LCD screen, the LG G4 goes one step further with something called an IPS Quantum display.
According to LG that makes it 20% richer and 25% brighter than the screen on the LG G3, which also improves outdoor visibility. Plus it has 50% greater contrast and consumes less power.
In reality the LG G4's screen is simply stunning and a huge improvement over the LG G3's rather dark screen.
It's also 98% compliant with DCI (digital cinema initiatives), making it almost the same class as a cinema screen. This means colours look rich and vibrant, and thanks to the curved display that uses reinforced glass, it makes it (according to LG's numbers) 30% more robust.
That's all very good news, because as impressive as the LG G3's screen is resolution-wise it's not perfect and in particular suffers from a drop off in brightness when not viewed straight on.
Power and storage
LG has made the slightly surprising decision to use the 1.8GHz hexa-core Snapdragon 808 in the LG G4, rather than the octa-core Snapdragon 810 favoured by the likes of the HTC One M9.
Despite being a slightly lower end chip LG promises no slowdown and given that it's coupled with 3GB of RAM we can believe that.
The LG G3 wasn't exactly lacking for power either, with its 2.5GHz quad-core Snapdragon 801 processor and 2GB of RAM, but we did notice some lag in the interface. The LG G4 has the older handset well beat in the performance stakes, with the lag that plagued the LG G3 absent from the G4.
Storage is a real highlight of the G4, as not only does it have 32GB built in, but it has a microSD card slot and supports up to 200GB of expansion. That's a whole lot of space.
The 16GB LG G3 can't quite match that, but it supports a respectable 128GB of expansion with a microSD card.
LG has big camera ambitions - that was clear from the LG G3 - and it's even more so with the LG G4. The G3 has a 13MP snapper with optical image stabilisation and a laser autofocus for instant focusing.
But the LG G4 has a 16MP sensor with an f/1.8 lens aperture, which is a big improvement on the G3's f/2.4 aperture and allows far more light in for superior low-light performance.
Like the LG G3 it has optical image stabilisation, but it's better than ever in the LG G4 with a higher tolerance for shaking, so images come out sharp and blur free.
The LG G4 also has some fancy new modes and features, like light and object recognition, lots of manual mode options to give you more control and options like 'Quick Shot', which lets you take a photo by double tapping the rear key even when the phone is locked.
If the LG G4 isn't locked, then it lets you load the camera in just 0.6 seconds, making it one of the fastest smartphones for picking up and shooting, although when it is locked this time extends to 2 seconds.
In practise the LG G4 has a fantastic camera that compares favourably to other flagship handsets like the Samsung Galaxy S6 and iPhone 6.
The LG G4's camera performs very well in low light conditions, but in bright scenes it really impresses, and although the LG G3's camera is no slouch, the newer handset's snapper is a clear improvement.
The LG G4's front-facing camera is an upgrade over the G3's too, as while the LG G3 has just a 2.1MP sensor the LG G4 has an 8MP wide-angle one.
On paper the battery should be exactly the same in each phone, as both the LG G4 and the LG G3 have 3000mAh juice packs, and in an increasingly rare move both are removable.
We were hopeful that the LG G4 would have longer life than the G3, as while there's no change to the battery the G4 should be less power hungry and offer a more efficient processor too.
However we found that the LG G4 is just as poor at holding on to its charge as the LG G3, with a full day of moderate use leaving the G4 with just 15% battery and sometimes less.
The demanding high resolution screen can shoulder a lot of the blame for this, but it seems that the LG G4 hasn't been optimised as well as the G3, meaning that the older handset has the edge when it comes to holding on to its battery. Hopefully LG will release software improvements soon that will eke out more battery from the G4.
Some versions of the LG G3 also came with wireless charging features, something that is sadly missing from the LG G4.
Most of the features that we haven't already mentioned are aspects of the interface. The LG G4 takes most of the good stuff from the G3, but adds new things like Smart Board, which combines key information from various apps and displays it all on a single widget, and Smart Alert, which provides activity suggestions based on the weather, your location and your interests.
Both phones also feature LG's innovative rear key, which is designed to be easier to hit than side-mounted buttons but can take a bit of getting used to.
The LG G4 was always almost guaranteed to be a better phone than the LG G3 on the strength of its specs and features, and now that we've had a chance to try out the LG G4 we can confirm that it is indeed a more accomplished smartphone.
More importantly it has fixed some of the biggest issues with LG's last handset, such as its slightly disappointing screen and not particularly premium design.
The LG G3 will still be available to buy for the next year or so, and will cost a lot less too - so if you're desperate to buy something from the double-lettered brand, check out our review of the LG G4 before making a decision over which LG is the handset for you.