[Nexus Player Q&A, Help & Troubleshooting] Haggster66:
I would've said the same, prior to the Marshmallow upgrade; whether the Cast icon would appear in Cast enabled apps was a matter of pure luck, as well as the "cast screen to" feature on Android devices. I got a lot of Cast connection losses as well, while the content was then still playing on the TV, without any possibility to control it (other than stopping it via the Nexus Player remote).

But all of those issues are fixed now with the Marshmallow upgrade (and I guess the various Google Cast Receiver app updates, that have been released since then).

The one thing that I find absolutely unacceptable is the following fact which you have mentioned as well: That the Nexus Player seems to be a 2nd class Google Cast device, which is e.g. not supported by Spotify, while working perfectly fine on Chromecasts. Google is allowing fragmentation of their Cast ecosystem because of this and this might be the beginning of the end of its acceptance, especially when it comes to Smart TVs that are shipped with Android TV and for which all companies involved are especially advertising the Cast functionality.

To the user who mentioned that both, the Nexus Player and the Chromecast are loading/streaming faster over Ethernet than over Wi-Fi: I strongly doubt that this is the case, especially since, as mentioned above, the available Ethernet adapters are only USB 2.0 capable. If you're talking about an Nvidia Shield TV I'd believe you, since that one supports Gigabit Ethernet natively, but regarding Chromecasts and Nexus Players... maybe if your wi-fi is horrible or you're using 2.4GHz wi-fi only... otherwise...no, not at all.

Anyway, since the original question was something like "Chromecast vs. Nexus Player": I have both, and I fully replaced my Chromecast with my Nexus Player since I have found that it makes the Chromecast redundant.

Some advantages of the Chromecast that should be considered:

-It's perfectly suited for taking it with you when traveling, while the Nexus Player is more of a fixed device that you set up once, connect it to your TV and leave it there.

- The Chromecast might reboot a couple of seconds faster than the Nexus Player, in case you shut off your devices often.

- The Chromecast allows you to adjust the backdrop e.g. with weather data and specific background images; the similar looking stock-backdrop of the Nexus Player cannot be modified at all.

- The Nexus Player wants you to sign into a specific Google account, whereas the Chromecast only requires you to set up a wi-fi.

- Chromecast doesn't need a wall socket and can be powered by your TV's USB port (even though using a real power adapter is recommended due to stability reasons).

- As mentioned, Chromecast isn't treated as a 2nd class Cast device by e.g. HBO (lol) and Spotify.

- You won't have to deal with yet another remote control in addition to your TV's, your audio system's and what-not remote controls, if using a Chromecast

- Google so far hasn't dared to release a firmware upgrade for the Chromecast which increases the brightness to a bazillion % and causes all blacks to look washed-out as hell.

I'm not gonna mention any advantages of the Nexus Player here as I've already said that I, personally, prefer the Nexus Player; I think it comes down to personal preferences regarding the above-points. Some things might be more important to some people, while others aren't, the same goes for what compromises are acceptable to the specific user.