The ending is the best part. Particularly the last few panels will probably stick with a reader forever.
As I understand it, the first volume of the Invisibles is purchased something along the lines of an order of magnitude more than the rest put together, usually because people love Grant Morrison's superheroics* or have been captured by his reputation, but wind up disliking Invisibles because it's somewhat incoherent pretty much straight through, and initially rather opaque about what it's doing.
So, it's really not for everybody, and it's a pretty major investment of time and effort.
That said, it's really good, in that it's really entertaining and life-affirming and all that great shit people go to Grant Morrison for. It's not as good as The Filth, Flex Mentallo, or maybe even Animal Man, so I can only conclude its undeserved reputation as his best work stems largely from the fact it's longer than any of those; but it is fairly up there in his great works.
If you liked the first volume, which is possibly the least interesting, then you should like the later ones. (Although iirc vol. 2 is a bit slower than the others. Or maybe it doesn't. Which one opens with King Mob getting interrogated? Because that was pretty cool.)
It's actually a lot like Final Crisis (like, a lot like Final Crisis, really--the plot of Final Crisis is effectively the plot from Invisibles, substituting Darkseid for the Outer Church). Of course, when I say it was like Final Crisis, I mean if Final Crisis were stretched out to a point where it made a modicum of sense and didn't suck in general.
