Instead of felguard you get a imp that summons more imps every felfirebolt. Imp me daddyThe main draw, for me at least, is going to be the ability to experiment with new combinations of talent choices. I think we can all be honest and acknowledge that there will be meta builds, and that this is inevitable; however, I think the option to be able to granularly customize some hyper-specialized, dumb builds is important in an MMO (like a modern-age Shockadin build).
For instance, imagine if it was possible to make a Demonology Warlock build that could give up all major cooldowns in lieu of summoning more imps and gave you the ability to increase the power of your main Imp pet instead of your Felguard. That would be a fun idea for a build, but would be awful and off meta. But even if it's off meta, who would want to stop an aspiring Gnome Warlock from attaining a personal title of "The Implord" on an RP server? As someone who has played OSRS and other games where someone else making the wrong choice doesn't necessarily affect you, it's always fun to see a "cute noob" that's doing something that's in every way wrong.