Annihilation was top notch.
The Mini's leading to it were less so, but still good overall.
The mini's leading to Annihilation : Conquest (Which is for all intentive purposes is Annihilation II) were good.
Annihilation : Conquest was good as well.
The problem with Conquest was that the scope and storytelling was no where near that of the original Annihilation, which everyone compared it to. Not that it's a bad thing, because it pretty much is a direct sequel to the first.
Nova, which spun out of Annihilation, has had a very solid first 15 issues, and is definatly worth it.
Guardians of the Galaxy, which spun out of Annihilation : Conquest, is kicking more ass than most books and it's only at it's 4th issue. The only thing I can see wrong with Guardians of the Galaxy is that if you didnt read through Annihilation:Conquest, you might be a little confused and lost.
I definatly suggest the entire "Annihilation" saga to anyone that hasn't read it. The mini's leading up to the original, the original, Nova spinning out, the mini's / tie-ins leading up to Conquest, Conquest itself, and Guardians. Marvel really did bring their cosmic game back with a bang with Annihilation, and Conquest kept it moving along. I wish they'd do a third one, as a trilogy of sorts, but they're running with War of the Kings instead next season.
Hope that helps you.