Perhaps not too extreme, but comparing it to the original series, it was far darker and more edgier in the way it approached things. Especially when you consider the original idea the network gave Bruce Timm and co. Was to make a a teen batman that kids could relate to. (that's teen Bruce, mind you. In High school.) Like, almost half of Terry's rogues gallery would die. (or suffer fates worse than death)
Also, the cyberpunkish setting and style really feels 90's, where it was still something that was "edgy" and "dark".
or maybe I just dont know what im talking about, but whatever the case may be I loved the fuck out of Batman Beyond. Its a pity how underutilized it is by DC. I mean, the beyond universe, or rather, a similar one- was canonized to the comics, but either way it gets such rare love.