Except that it looked just like BATMAN: THE KILLING JOKE, and the SUPERMAN ANNUAL Moore and Gibbons collaborated on before doing WATCHMEN.

I don't think there is anything particularly beautiful or exceptional on Gibbons' end of the collaboration. It is completely an Alan Moore tour de force that Gibbons was fortunate to be invited to be a part of.
Without that one collaboration, we probably would remember Gibbons as a third-rate illustrator on a par with guys like Joe Staton, Dan Spiegle, Pay Boyette, Ruben Yandoc and Tom Mandrake. Guys who have done some pleasant work, but are a far cry from guys like Gary Leach, Alan Davis, Bissette/Tottleben, Perez, Miller, Simonson, Giffen, Bolland, Bolton, Russell, Starlin and other top-tier innovative comics artists.

I respect the thought and concept that went into WATCHMEN by Gibbons. But it's just like those BRAVE AND THE BOLD issues by Bob Haney and Neal Adams. Whatever Haney's labors or intent, it was completely a Neal Adams show, and they are Adams issues in the eyes of any collector. Gibbons' linestyle is bland and unspectacular. Whether Gibbons planned it to be that way for WATCHMEN, Gibbons' art already was that for many years anyway.