Just talked about the new Echo Plus in the Philips Hue bulbs thread.
In a short, IMO based on what I’ve experienced, it does not replace the Hue Bridge (if you have or want Hue bulbs, get the Hue Bridge) and it’s really just a more expensive Echo.
That said, it does have a 0.8" tweeter versus the 0.6" tweeter on the standard Echo. I haven’t noticed any differences yet. I have read reviews where people said that it sacrifices bass for treble, but I don’t know if that’s actually true.