[Samsung Galaxy Alpha] symphara:
As promised, here's an update to my original post, having used the phone for a couple of weeks now.

1. Battery life is better than expected and actually good, at least for my use. So far it hasn't died on me, not even after fairly extensive daily use (navigation/web). The power saving mode noticeably reduces the power drain without worsening performance too much. To date I was never in a situation where I had to use the "ultra" power saving mode. A quick example: in 24 hours, out of which 11 were in flight mode, it went from 100% to 63%, with moderate-light use. It charges very quickly. Mine doesn't heat up, no matter what I do.

2. The fingerprint scanner works reliably only when swiping vertically. It's very unreliable if I try to register oblique swipes. This makes it impractical to use with only one hand, and unlock with my thumb. I need to hold the phone with one hand and unlock with the other. Clearly TouchID (which I tried) and perhaps the new S6 sensor (which I haven't tried) are better. TouchID for sure works in varying directions and is suitable for one-handed unlock.

3. GPS location tracking is not as good as expected. It has significant problems in cities. On the train it can get location lock only close to the window. Location updating is not smooth when moving at speed. Compared to my iPad, when used side-by-side, the difference in the quality of implementation (speed of lock, smoothness of update, precision) is very large.

4. The camera is only good in good light. The performance degrades steadily with the amount of available light, to the point where it is terrible in low light (e.g. city night shots, intimate restaurant). The camera app is very good in my opinion. I am particularly impressed with the panorama shots: easy to take, very fast processing, good stitching.

5. Performance is a mixed bag, and for me, not quite satisfactory. For some things it's clearly fast - it records 60fps full HD beautifully, it plays Hearthstone very well (smoother than the 2014 Nexus 7 with Lollipop!), it downloads and installs things very fast, etc. Other applications and use-cases are not so lucky.

Chrome frequently staggers, to the point of not accepting scroll input for periods of nearly 1 second now and again. App switching is always slow. Google Maps is fairly slow and often jerky. Performance does seem to degrade over time, so periodic closures of apps are needed. It's good that it provides a "close all" option.

The worst thing is that overall the phone does not give an even, smooth performance. In my opinion, Nexus 4 with Lollipop gives a better overall software experience even if it cannot satisfy performance-hungry applications (which the Galaxy Alpha can), but it's much more fluid overall. My wife's Nexus 5, which I think is inferior to the Alpha in terms of CPU, gives a significantly better overall software experience - it's faster to do pretty much anything, and very fluid.

I am waiting with considerable interest the Lollipop update on this phone. If it elevates the software experience closer to the level of the Nexus, it would make the phone very enjoyable to use. As it stands, the hardware feels premium but the software experience definitely gives a feel of a low-mid range device to me. Considering what I paid for it, it's still not a bad deal, but it falls well short of the intended Samsung near-flagship positioning. Interestingly, mutatis mutandis, the old Nexus 5 does almost everything better than the Alpha, including better low-light camera performance.