I really dig it. PCs really need to think about what magic items they pick up. The limit of three, since not every magic item calls for attunement, is fine by me.
I like the concept of attunement in that attuning to a magical sword unlocks its greater magical powers, but part of me doesn't like it or doesn't like the limit of 3. Really though, I think we need to see some higher level play with more items before I can have a proper opinion on it.