That's a yes and a no. Depends on what you look at. Graphically the game has aged, and so are the controls after MK Wii introduced better controls, even though they're still solid. Only thing that holds up graphically are the character models, that are sprites instead of 3D models. The items are the best in the series, but no doubt it has the best tracks, battle and race. The race tracks gave you lots of options for shortcuts, sometimes with a tradeoff, sometimes not, battle tracks altitude differences that could give you an upper hand and situations changed quickly. It's pretty much what an arcade racer should be. MK8 is pretty much the opposite to MK64. 

I still hope that Nintendo will announce more tracks, but eh... I suppose DLC is also good, because the DLC price is REALLY low by what they actually offer you.

Also.. this will be kinda odd to see WII U MK players playing online for free whereas Switch user have to pay.

Omg I know. A couple of months ago, my best friend and I decided to take a break from Mario Kart Wii and Mario Kart 8 by switching it up a bit with MK64 on my N64. The textures were so bad on an HD TV that it hurt our eyes and we couldn't get through more than one Grand Prix...

Very nice, this is the battle mode the original MK8 should have had.

Who knows when the Wii U will stop their online features (Probably before 2020). And Switch owners gets the luxury to play it on the go. MK7 to MK8 Deluxe is such a massive improvement. 

You should play it on SDTV, like it's supposed to.