Why is Rock Band 4 not critically acclaimed at all?

I've played Rock Band 4 before. Honestly, it is not good. Rock Band 1 and 2 tower above it (maybe less for 3). First, the song list is not interesting and (in my honest opinion) there are no 'hits' or 'classics' that we would know about - with the lone exception of Van Halen's "Panama". Second, the character customisation falls short of its predecessors - it just feels like you're customising a mold as opposed to making something original.

Let's just say the gameplay experience is bad enough that I stopped playing it after going through it twice and stuck with the older games.