High-quality excitation-energy spectra of 7ΛLi, 9ΛBe, 13ΛC and 16ΛO as well as 12ΛC have been obtained with 2 MeV (FWHM) resolution and good statistics through the (π+, K+) reaction. The spectra of 12ΛC, 16Λ and 13ΛC are discussed in relation to the ΛN spin-dependent interaction, and those of 9ΛBe and 7ΛLi within the framework of the cluster structure of Λ hypernuclei. It is emphasized that Λ hypernuclear spectroscopy provides us with valuable information on Λ hypernuclear structure and the ΛN interaction.