I have used the OnePlus One for slightly over a week. Here are my impressions.
It is Big
It is slightly longer than a pen, but it sticks out everywhere. See picture below. Depending on my shirt pocket, it sticks out about 1 or 2 cm out of my shirt pocket. When I am self conscious about it, I put it my pants. Then it pokes against my hip. In my jeans where the pockets are shallower, no I am not happy to see you, it is just my OPO. The width of the phone is such that the Google Now button has been remapped from the Menu to the Home button. The menu button is too far to reach without some finger gymnastics.
The case shown here is from Sim Lim Square. Its long edge protection is poor. I have since replaced it with a Diztronic (excellent!) purchased from HardWareZone.
Battery life is great
It can easily last a full 24 hours with 3 hrs of Screen On Time. Not that I am holding back my usage of anything.
Wireless is weird
I ported my Llama profiles from my Galaxy S2 9100. This has been working fine for months.
WiFi control does not work reliably on the OnePlus One. Often than not the WiFi locks up. The button changes from a blue to white with a red outline. The only way to clear this is wait overnight or restart. After I rooted, the WiFi switch on-off-on is much better. A case for root? The home AP, I have changed the country and zone to avoid interference from my neighbours and it caused the OnePlus One to hang! Really strange. Changed the country and code back. Now Llama is controlling it smoothly.
The screen is great
5.5 inches with a 3100mAh battery. Enough said.