I'm not really contributing much here. I do want to say that I've been reading all these comments. I'm so bummed that Harmonix has seemingly messed this one up. I LOVE Rock Band, and Guitar Hero. I play drums in real life. I love these rhythm games. My buddy picked this up. I have held off. I am so glad I did. Harmonix is a company who cared SO MUCH about quality and the experience. How could they release this with so many things "not ready". HOW IS THERE NO ONLINE MULTIPLAYER???? I am seriously baffled by this. I LOVED going online to play random songs with random people. It was great jamming and trying to not screw the song up. I'm surprised by these guys. It's not like them. Also, I'm not picking this game up until my ION kit from my 360 is compatible with Xbox One.
The game feels like it has a fraction of the budget of the prior games, which makes sense, since prior games had more substantial publisher backing from EA and MTV. So I don't necessarily fault Harmonix for not having some of these features available at launch, but at the same time, this is normally a $60 game (and much more with the instrument bundles), so it's certainly not unreasonable for consumers to expect a product that has at minimum feature parity with its predecessors. As it stands, Rock Band 3 feels like a much more complete game and perhaps remains the best Rock Band experience. The issue of course is people are moving on to current gen consoles and don't have a last gen system (or don't want to get it out of storage) to play old Rock Band games, and this is essentially the justification for Rock Band 4's existence.
I'd say to Harmonix's credit, they definitely did try to get as much support for old instruments as they could, and support for previously bought DLC (granted the process of finding all your old DLC on the platform is almost more trouble than its worth). Unfortunately, Rock Band 4's offerings feel fairly barebones right now, but I am hopeful they will continue to work on this for the December update and beyond. And barebones or not, it still feels like good old Rock Band when I'm actually jamming out to my favorite songs, and I am grateful there's a current gen way to do so now.