HTC ditched the Ultrapixels for the One M9's rear camera and gave it a more conventional 20MP snapper. The results were strong, but not a match for rivals like the Samsung Galaxy S6 and LG G4, though sticking a 4 Ultrapixel sensor on the front was a smart move.
The HTC 10 should be a significant improvement, thanks to a 12MP camera on the back, which uses Ultrapixels to let more light in, and optical image stabilisation to keep shots focused.
The 5MP front-facing camera sounds promising as well, as it too has optical image stabilisation, which is a first for a front-facing smartphone snapper. Not only should shots be good, but the camera on the HTC 10 is designed to focus and shoot fast and even launching it apparently takes just 0.6 seconds.
The HTC 10 has a 3000mAh battery, which makes for a small boost on the 2840mAh juice pack in the HTC One M9. It's not as big of an upgrade as we'd hoped, as the HTC One M9 could struggle to last a day if you used it heavily and the HTC 10 has a larger, higher resolution screen to light up.
But despite that HTC claims it can keep going for up to two days, thanks to a 'Boost+' feature which can automatically optimise your memory, ensure less battery is used during gameplay, and auto detect and shut down apps that use excessive power, improving life by up to 30% in the process.
The HTC 10 also supports QuickCharge 3.0, allowing you to charge the battery up to 50% in just 30 minutes. The HTC One M9 also supports fast charging, though it uses the older QuickCharge 2.0. Yet despite that it can actually reach 60% life in the same amount of time.
As well as aesthetics HTC tends to put a big focus on audio. You can see that in the HTC One M9, with its dual front-facing BoomSound speakers pumping out crisp sound.
But it's better still on the HTC 10. The BoomSound speakers are back, but this year HTC's flagship also supports 24-bit Hi-Res audio and has a Personal Audio Profile system, which adjusts the sound frequencies based on your hearing, so music always sounds as it should.
There's just one front facing speaker here, with the second bass speaker moving to the base of the HTC 10. BoomSound is now BoomSound Hi-Fi Edition too, with dedicated amps for each speaker and the headphone jack.
Release date and price
The HTC One M9 is available now and will set you back roughly £370 (US$400, AU$600) SIM free. The HTC 10 will be available from May, while It's not yet been confirmed what it will cost.
As a brand new flagship though it's sure to be significantly more expensive. We'd guess around £570/$750/AU$1,150.
On paper the HTC 10 is exactly the phone HTC needed and a huge upgrade on the HTC One M9. It's not just more powerful, but also has a refreshed design, a far better screen, an impressive camera, better audio, a bigger battery and new features like a fingerprint scanner.
If you're buying a phone now and have the money to spare it's the clear choice over the HTC One M9. If you already have an M9 the HTC 10 is probably not worth upgrading to, as that phone is still beautiful and powerful, but if you just can't resist you probably won't regret it.
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James is a freelance phones, tablets and wearables writer and sub-editor at TechRadar. He has a love for everything ‘smart’, from watches to lights, and can often be found arguing with AI assistants or drowning in the latest apps. James also contributes to 3G.co.uk, 4G.co.uk and 5G.co.uk and has written for T3, Digital Camera World, Clarity Media and others, with work on the web, in print and on TV.