Mass Effect 3 covered plenty of bases, but we still felt that too many aliens got ignored. We'd love to see more of the Asari and Salarians in the next wave of DLC, and that's without touching the huge selection of barely-touched races. The Hanar and Elcor barely make a cameo in Mass Effect 3, aside from the excellent BLASTO! audio episodes.
Maybe we're all just being too nice, but we think too many races have been given a rough deal - the Vorcha seem incapable of doing anything that doesn't revolve around crime, but the history of the Batarians is far more interesting. After centuries of building up their reputation on the Citadel, their plans were scuppered by humanity's sudden technological leaps. The Batarian and human races are based relatively close to each other in the galaxy, forcing them to compete for nearby areas and resources.
After the discovery of Mass Effect technology on Mars, humanity quickly zoomed ahead, shafting the future of the Batarians in the process. So far we've only seen their race painted as terrorist scum, but we think there's a more interesting story to tell. Regardless of which races get focussed on next, we'd like to see life outside of the Citadel: Take us to your leader.