His first 4 shows had definite talent (haven't seen much of All That, but I know I'd enjoy it from what I HAVE seen), although I think Drake and Josh was his high point.. iCarly started off good, but by the end, it wasn't worth watching, in my opinion. Anything after that is just a downhill decline.
I remember LOVING The Amanda Show as a kid, should eventually rewatch that.
Here's how I'd rank them from favorite to least favorite:
Drake and Josh
The Amanda Show
Kenan and Kel
Henry Danger (even though I've only seen a few episodes)
Sam & Cat
I didn't watch Game Shakers past the first ep, but it wasn't that good IMO.