I have noticed that playing music from Pandora runs the battery down. I'm listening to Pandora on my phone with a plug-in headset (Bose) so there is no Bluetooth contention between the watch and the headset.
The difference is dramatic. If I don't listen to music at all, the watch will have 40-60% battery at 10pm (starting at 7am). If I listen to music at work (starting at around 8 am) the watch is dead by 5pm. My guess is that there are a lot of notifications going to the watch when playing music on Pandora and it's the data comm between the phone and watch that is causing the battery to be used excessively.
I tried adding Pandora to the 'Blocked Notification' list in Androidwear on the phone but that stop the phone from sending what music is playing on Pandora and did not stop the battery from running down either. My solution was to by a Aukey wireless charging pad (from Amazon, plug) for work and charge the watch back up mid-day.
I haven't had a chance to really test Google Play, but my guess is that it will have the same problem because it's not the apps, it's the notifications (just to many of 'em) that are causing the battery drain. I'll try that and update later.
Update: 2015-03-30
I have found that the watch cannot go more than two days without a restart, I have found that if I restart the watch as I put it on the charger every evening, I have consistent, normal battery usage the next day.
If I let the watch run without a restart and just charge it every night, sometime on the third day the watch will quickly run the battery down to auto-shutdown (or crash).
There are clearly some resource leaks. The question is which app(s) are at fault or is the os. Time will tell (unintended pun stumbled upon).
I've also come to the realization that the accelerometer is to sensitive and activates the watch far more than needed. I come to this conclusion by using the Theater mode which requires me to press the button on the side of the watch to light it up. When in this mode, the watch can have well over 50% battery life at the end of the day.
I don't know, but I hope that things will improve over time. I have an HTC One/M7 and don't have Lollipop yet. I have heard that AndroidWear integration is better with the newer OS.
Update 2015-06-18
Update: I got a Galaxy S6 Edge (with Lollipop) about a month ago and with the new phone OS I got updates to the watch OS as well. I now have three choices for "Interruptions"; Show All, Priority Only and None. With KitKatt it was only Show All or None. But I digress, the battery life of the watch is much improved wit Lollipop; I can get through an entire day without the watch running the battery down to zero. If you haven't already, get Lollipop on your phone to get things going.
One other note, when I upgraded. The Pandora app on my phone no longer works with my watch. With KitKatt I could see artists and skip forward, etc. With Lollipop... nothing. I've reinstalled Pandora but still nothing but that's for another thread.