There's no point in reiterating the praise for this miniseries. Many have called it the best television production ever, and as far as I can tell, they're absolutely correct. This is (NBC notwithstanding) the true definition of 'must-see TV'.
I just want to comment on something that struck me when I watched this recently on DVD. There's no way that an actor like Michael Gambon could ever get cast as the leading man in an American production (for TV or movies). He's just not physically attractive enough in the conventional sense; for example, he has the beginnings of a double-chin (more of a sloping-down from his chin to his collar), and I can't imagine any American producer being willing to give such an "not hot" actor so much screen time in the lead role.
Yet, it hardly needs be said, he is 100% perfect in this role, and it's hard to imagine anyone else doing as good a job. He can convey more feeling (rage, helplessness, love, hatred) in one close-up of his eyes than some actors do in their entire careers. His presence in this film is, in a sense, a reminder of how lucky we all are that it ever got made at all, by a BBC that was willing to give producer Kenith Trodd almost complete autonomy, as long as he stayed within budget. With the possible exception of HBO, you just don't see that sort of artistic freedom too often over on this side of the pond.
Anyway, as others said, it's a masterpiece, brilliantly written and brilliantly acted. Truly one of the most incredible uses of the television medium ever.