that this is a cadillac is similar to peter jackson getting the oscar for 'return of the king' only. the wrap up to the 'planetary' series had to be stunning, though not necessarily the strongest of the franchise.
while the ultimate ending to planetary contained in vol.4 ('spacetime archeology') was a let down, IMHO, each discreet episode was impressive, and well worth the wait.
much of the strength of the series lies in its exploration of popular comic book and adventure literature tropes (a la League of Extraordinary Gentlemen, but more diverse), stitched into the fabric of a unique reality ('planetary' organization as hunters of the 20th Century's lost or hidden history). the whole series was such an epic and original read, and pretty much my introduction to ellis' genius.
'planetary' collections one through four are as good as it gets if you want to see the vanguard of the genre, and where comic book tropes may take us in the future. a grand and unparalleled series, though without a closure that equaled the rest of the story arc.