The Ibn Ezra (Koheles 5) criticizes the Piyutim of the Kalir.*
He has four main complaints against them.
1) Most of them are Chidos (riddles) & Mosholim (parables)
2) Instead of Loshon Hakodesh he mixes in Loshon Hatalmud
3) He invents words & uses improper Dikduk (poetic licence)
4) They are based on Medroshos & Agodos instead of Pshat
The Teshuvas Maharashdam (O..Ch 35) claims,
The Sephardic Paytonim have a simpler and easier
language. Everybody can understand the Piyut, whereas the
Ashkenazi Paytonim use difficult words and even the
Shatz (Chazzan) doesn't understand what he is saying.
He recommends Ashkenazim to switch to Nusach Sefard,
which is a superior Nusach. He claims "Al Titosh Toras
Imecha is only applicable when there is a small Issur involved
and not for changing a Nusach Hatefilah.
The Chasam Sofer (Hagohos O.Ch.68) writes that "the Mahrashdam
wasn't aware of the Magen Avraham (68) who writes. you are
not allowed to change the Nusach Hatefilah because
there are 12 gates in heaven, one for each Shevet. Each one
has his own Minhag. The Yerushalmi says, they are all equal
you should not change from the Minhag of your fathers."
Had the Maharshdam been aware of this M.A., he wouldn't
have written what he wrote".
*R' Eliezer Hakalir