Now that it's officially out, I can give my full impressions.
Personally, I don't like the design. Not because it's ugly. It's because due to the obvious resemblance to the iPhone 6, it looks somewhat uninspired. Many "iPhone-inspired" phones have their own design changes, so they don't look that similar. HTC's A9 is more-or-less like an iPhone clone, apart from the camera placement and the front. I'm pretty sure that there are some out there who like the design and I don't fault them. I just feel that HTC lost its sense of unique design, which makes me feel rather sad. (Before you say Apple copied HTC, the iPhone 6 only had a similar antenna band design to the M7. The rest of the phone took design cues from the 5th generation iPod touch). The bezels also looks a bit too thick for my liking.
In terms of hardware, it's pretty solid. SD617, 3GB of RAM with the 32GB model, 1080p AMOLED display, 24-bit/192KHz audio support and all that. Nothing to write home about. Capable hardware that's decidedly upper-midrange, exactly the point of the A9.
Instead, the main pros of this phone come from the software. Sense has been lightened and resembles stock Android more. HTC is also promising updates within 15 days after Nexus phones, which is very bold and we'll see if they can keep their promise. Aside from that, Sense is snappy, responsive and largely clutter-free.
We'll have to wait to get a final verdict.