Their charm is based precisely on not being innovative, but on consistently providing a steady diet of bluesy boogie-rock year in and year out for 40+ years.
Well, a lot of ZZ Top purtists hate the synthesizer stuff... it’s still controversial for some
IMHO they pushed the envelope in a number of directions over the years without losing touch of the root sound- but I definitely consider them innovative, particularly withing this genre- vs say, the Fab T Birds for Stevie Ray Vaughn