Infinity War had a much different job, in that it had to bring together all the different characters and pieces of the MCU into one film, whereas Black Panther is mostly a standalone story about Wakanda. Infinity War relies on the fact that you've had 17 previous films setting the board for the big game, whereas Black Panther is playing its own game. So that's not the same design at all. Both are of course equally valid but it makes comparisons between the two a little uneven.
I do think that that differentiation largely accounts for Black Panther's ability to expand upon the typical MCU audience, because you don't have to have seen the other films in order to understand it. Infinity War is much more strictly for preexisting fans.
I think that's what is largely getting missed by the folks panning it here or saying that it doesn't live up to the hype.
Those folks, like me, aren't the target audience. BP did something remarkable and it's hard for people already in the mix to see: Without major backlash BP massively infused a whole new perspective and increased the cultural audience invited under the tent. Sure there was a couple heroes who weren't the standard strong white male, but BP exploded that and made PoC full fledged equals. And in some cases better than the existing squad.
Representation matters. It's to that 8 year old kid who finally gets to see strong and smart characters that look a lot more like him than the rest of the universe doe who it matters most to. Not to folks like me. Although a lot of folks like me really dug it. =)
And it did it without offending or lampooning anyone.
That's incredible.