Read it in grad school (for an English PhD). And honestly, that's the only context in which I'd recommend doing so. It's a dreary slog of a book; we were reading it more for its historical importance than for any particular literary quality.

But I don't recall anyone at the time (mid 90s) doubting that the book was a forgery -- a somewhat inept mish-mash of Celtic literary figures and motifs. The interesting part was that people went absolutely wild for it. To the point that one can now speak of "Ossianism" as a significant literary movement.