Heard great things. May well give that a go. Worthwhile?
It's the definition of epic. If you like a darker and grittier (and sometimes downright lunatic) Batman, Miller's version is the way to go.
Chronologically, the Miller Batman goes (it's technically a separate universe from the main DC titles):
Batman - Year One (Batman #404-407)
All-Star Batman & Robin, the Boy Wonder (#1-10)
Spawn/Batman #1
The Dark Knight Returns (#1-4)
The Dark Knight Strikes Again (#1-3)
The Dark Knight III - The Master Race (#1-8)
All are available in TPB. Be sure to check out the Absolute All-Star Batman & Robin, the Boy Wonder Hardcover so you can read all ten issues (the first AS Batman & Robin HC/TPB collection only collected issues #1-9 due to the delay with #10).
Spawn/Batman isn't an essential read and it's never been collected in trade, though it's easy to find online or even at a local comic shop's back issue bins, and for pretty cheap. Like I said, not essential to that Batman mythology, but it is a part of the Miller Batman canon, along with everything else listed above.