Being dead honest, I've barely played the modern version of this so this rating isn't really much for it.
I played A Lot of this around 2006-10 tho, maybe even earlier. At least early enough that Knuckles still had the really fucked up wall climbing sprites and jumping on the roof of that house in the first level sent you to hell. Also remember Zim's house being an official mp level in it and spending a lot of time on servers running that.
Still had an insane amount of fun with all the mods and hangout servers back then tho.