I think Millar's run get's a split reception, some people say it's great some people say otherwise.
I actually think Scott Snyder's run got (The slightest bit) better as the series progressed.
I liked the issue where Alec Holland travels to Abigail Arcane's hometown, and the final main story arc, that takes Swamp Thing to an alternate timeline, where The Rot has taken over the world. The dystopian alternate reality trope has been done to death, and this storyline is not amazing or anything, but I thought it was pretty good, it get's rid of many of the problems that have plagued the previous issues of Scott Snyder's run.