Asia de Cuba, as the name suggests, is more fusion than Cuban. But it has a pretty solid reputation (not that I've actually been).

I've been to both branches of Cafe Con Leche on the UWS, and was satisfied, but, like the OP, not overwhelmed.

newyorkmetro.com (the online arm of New York Magazine) lists 45 restaurants under the "Latin American" category, which includes Cuban and other Latin cuisines. Several earn a "Critic's Pick" designation, including:

Victor's Cafe on the west side of Midtown
Little Havana in the West Village
and
La Flor de Broadway in Harlem

I haven't been to any of them, unfortunately.