On the contrary -- I felt this was a story in the classic Trek spirit, turning the 8472s from mere monsters into actual characters and embodying the idea that it's always possible to make peace and that most conflicts arise from misunderstandings. I don't agree that just being dangerous or menacing makes a species interesting.
As for telepathy, the only people who could receive 8472's telepathic communications were those who were themselves telepathic, Kes and Tuvok. Kes was gone by this point, and Tuvok wasn't on the mission to the biosphere (since his telepathy might've made him a security risk if they'd picked up his thoughts). As for the lack of telepathy between the 8472s, perhaps it was suppressed while they were in human form.