Never forget the fact that when they filmed
the end of season 4, there was going to be no season 5. At all. Consequently, the entire story had to be compressed frenetically, with several subplots suffering for it.
Also, understand that this ending was meant to be different. It was not to be some huge conflict resolved in yet another titanic battle. It was what Sheridan said - a war of ideology. It was the quintessential allegory to a very basic human struggle - chaos vs order. Heck... it's a struggle faced by the universe itself, right down to the creation of the stars.
As to the Shadows lacking a "face"... that I can understand. In one sense, that's what made TNG's "Best of Both Worlds" so haunting. To have Picard become a Borg, speaking in that mechanical voice, it was saying "this is your fate". However, consider this. The Vorlons all along manipulated the younger races in a genetic way so they'd appear as beautiful, similar creatures to those same races. The Shadows also used other races to do their bidding. This is why we see Morden, who in effect IS the Shadows face to the humans and other races. It was never their way to work openly until the time was right.