Volunteering at Alturas Sanctuary was a life-altering experience. It provided hands-on work (picking up poop, cleaning cages, doing more laundry than I ever would have expected, building toys, and feeding and transporting animals); education (about wildlife, the greater environment, and other ways of life); and fun (roaming around with other volunteers on days off, attending a concert, etc.). The environment was professional, safe, and comfortable (albeit be ready for some spiders and cold water showers).
The staff are overwhelmingly genuine, caring whole-heartedly about the well-being of the animals, while still taking the time to ensure that the volunteers weren't forgotten. The vet (Laura) would often share stories and answer questions during breaks - get to know her if you're logical, she's one of the coolest people I've ever encountered.
The animals are just as memorable. You'll build friendships quickly, and refer to them by name. I don't think I'll ever forget them.
My 3-week stay was during the busiest time of year, amid many changes (lack of dedicated coordinator, new volunteer house construction, etc.). This meant less organization, but going with the flow is all part of the Central American lifestyle. Although I found that some others had minor complaints, escalated items were addressed. The staff is there to help.
Be aware that the program is relatively new, but established. I expect that it will continue to develop. The owner shared goals regarding future projects, which I have high hopes for. While I'm extremely grateful for the experience I've already had, I'm definitely hoping to return.
It isn't a vacation; it's better. Go alone. Make friends (with people and animals). And use free time as an opportunity to learn and build relationships with those around you. It will change your life.