They just released a bunch of new apps to work with it. Netflix works great with it and I've only had a few issues w/ some Youtube videos, but that's not a big deal to me.
With a PC or Mac, you just need Chrome browser to play through. Chrome is my favorite browser so that's not an issue with us.
No iTunes support and I doubt that will ever happen, but there are other free music services (Pandora, Spotify) that work well with it.
I'm sure someone will come up with an app to play video and music files directly from you computer, but until then if you want to view videos on your computer, you have to upload them to Youtube first...I think.
Tablets and phones work great and I would say are easier to use than computers.
We have mostly Apple products in our house, so we may eventually get an Apple TV when the new one comes out. However, I've been very happy with the Chromecast (other than no iTunes ability) so we may end up skipping the Apple TV.