Alternative 4 is the only really inconsistent Anathema album, but the first half is the best material they have done so it offsets the lackluster second half somewhat. It should have been an ep, it would've been their best release.
I like Alternative 4 and Destiny (both in the second half of the CD), but I agree with you in general. Eternity's second half isn't that consistant though. The Silent Enigma is probably the most consistant that I've heard.