The biggest issue was trying to cram far, far too much into just three games, especially the last one.  The LoS universe was ripe for some brilliant ideas, but they weren't given enough time to be fully developed because a certain high-up in particular just wanted to wash his hands of the series.  I'd also love to see things such as the Founders game, or what happened to Victor - that could be a wonderfully fleshed out, full game in and of itself.  Victor being informed of his family's great heritage, and, guided by a mysterious man who visits him (Alucard in a guise as a human with powers, a la Genya Arikado), finds his family's old heirloom artifacts.  Along the way, he refines his prowess as a hunter, as his guide prepares him for a coming darkness.  In the end, he discovers that Alucard is the vampire who aided his ancestor Simon, but he doesn't know that Alucard is himself his ancestor.  I'd also love to know what Alucard got up to during the intervening years between him and Simon defeating Dracula, and the castle seige, and from then until the present day.  In that initial 500 years, there are multiple chances for a Belmont to come and face Dracula.  After then, lots of other potential vampires for the Belmonts to hunt, and other monsters across the world.  It also surprised me a lot that the Brotherhood didn't have nasty machinations going on in places, manipulating stuff behind the scenes, not just in relation to the fates of Gabriel, Marie, and Trevor.