Yeah, I remember that. I meant "like Rock Band" since there is no instrument support yet.
Actually, yes, there is guitar and bass support now, since the previous season.
On consoles, you need a compatible RB4 guitar (or the Riffmaster). On PC, I think you can use pretty much anything and map the buttons (Keyboard Hero?).
Also, even though it’s Harmonix, it is pretty featureless when compared with RB3 or RB4. You can't restart mid-song, co-op is very lame (you can't see other players' lanes), setlists are limited or nonexistent, there are no custom band members, no campaign, etc. It has improved a bit since it started but it's still very barebones. Hopefully, they revamp it or maybe let it have its own launcher separately. DLC is $5.
The pros: DLC is cross-platform, having Slipknot & System of a Down blasting on all these Zoomers and Alphas is wild. They have been updating it every couple of months with artist collaborations (Metallica is in Festival, but also in Racing & Battle Royale), and you can use the DLC songs as lobby tracks.
Festival is middling at best, but having Goku shred a solo while Vader slaps the bass, John Cena sings, and Spiderman hits the drums is a very weird experience. But having supported RB4 until the very end, I’m glad Harmonix and this genre are having a second wind on this platform.