I own a Gen 1 Echo Plus, along with a bunch of 2nd gen - and one 3rd gen - Echo Dots.
This newer model Plus replaced the old Gen 1 model in our living room, and the old model shifted into the kitchen - these two rooms are adjacent/open to each other, so having them near each other provides a decent sound experience. The newer Plus is noticeably clearer and has more depth in its sound quality when compared to the older Plus.
Other than better sound, the smaller form factor is great, and it's a nice bonus to have a built-in temperature sensor (although I'm not using this for anything right now).
One thing I've had trouble with is room awareness, which was fine before I shuffled the Echos around, but doesn't work at all now - i.e. walking into a room and saying "Alexa, turn the lights on" is met with a "Lights doesn't support that" response instead of her turning on the lights in the room she's in. I've tried a lot of stuff to troubleshoot this - including resetting all of the (Hue) lights and Echos in the house, and deleting/reinstalling all skills - but nothing has fixed it, so I'm at the stage where I'm going to have to reach out to Amazon for support.
Another thing I've had a little trouble with is the Bluetooth connection from my laptop to the newer Plus. This worked fine with the old Plus in the same spot, but it seems a bit flakier now including distorted sounds. My first attempt at a Bluetooth connection with the newer plus coincided with a Windows update, so it could very well be laptop-related rather than a problem with the Plus, but just mentioning it here in case.
Overall we're happy with this purchase, but we do miss the room awareness that installing this Plus seemed to throw out of wack.