I've only had my A9 for about a week, but I posted the following over at XDA. Some random thoughts in no particular order:
The interface has been very smooth, opening apps is quick, and memory management seems pretty solid. Browsing is good on wifi, but I haven't had a ton of time to try on LTE. Gaming is fair. I don't play that many games and the ones I do tend to be simpler fair (not much into 3d gaming). One candy crush-esque game that I play performs surprisingly poorly (doesn't deal well with a lot going on on screen at once) but it seems to be the exception.
Battery life is meh at best. Standby time is really solid. I only lose about 3% battery overnight, but the battery noticeably drops as the device gets used. It charges ridiculously quickly with a quick charge 2.0 charger though.
The camera has been okay. I'm not a huge shutterbug, but the pictures I've taken have been sufficient. I find it loses focus sometimes with last second movement (taking pic of my dogs can be difficult) but it seems good enough. A step up from the Xperia Z3 I had been using (automatic mode), a big step up from the Nexus 5, not as good as the Note 4.
The screen is a thing of beauty. I put it on sRGB mode and it's just perfect. Gets way bright, and gets dim enough in a dark room. I tend to keep it about 25% brightness and it works just fine for me.
Speaker sound is pretty good for a bottom mounted speaker. Nothing to write home about, but it gets the job done and is more than loud enough for my needs. Sound from the headphones is easily the best I've had from a smartphone. The tones are rich and thick, gets quite loud without distortion, and just sounds great. YMMV depending on your musical tastes, but it works great for classic rock, hard rock, metal, blues and jazz.
Fingerprint scanner has been flawless so far. I've added just my two thumbs, and it hasn't missed yet regardless of angle. It unlocks the phone quicker than I can adjust my hand to use it, so the speed is just right. I haven't used it for anything other than unlocking the device though.
Software is very on point. It has a lot of the simplicity of tock Android, but with Sense bells and whistles to up the game. I like the presentation. It feels very clean, intuitive and smooth. I miss the HTC Sense method of displaying recent apps, but other than that it seems like a good marriage of HTC and stock stylings. The theming engine is good, but slightly frustrating at times. I like the stock launcher and want to keep it, but the itch to modify more than what the theming allows for may prove too much.
It looks like an iPhone. HTC or anyone can spin it however they want, but it really does. I'm okay with that because I tend to think that the iPhone is an attractive design. That being said, when you hold it, it doesn't really feel like an iPhone. Compared to my wife's iPhone 6, it has a much more solid feel. It has better heft, feels a little sturdier, and has a really nice curve at the screen that your thumb just floats over. I'm not going to test the bendability of the device, but from feel alone I can't think of how it would bend without the use of tools. It really feels like an incredibly well made device, and it looks phenomenal.
All in all, I'm pretty happy with it so far. I think it's priced to high, but there really is a lot of quality here to enjoy. It's also the only device on the market that hits all of what I wanted in a device: 1) Amoled display. 2) Compact enough to use 1 handed. 3) 32 GB+ and SD Card expansion. 4) Premium build. 5) Stock or Light skin. 6) Rapid updates.