I would like an actually complete Apocalypse in addition to that. It was so good as it was, having an actual fully working version would give us something really solid to work from when griping about how these newfangled movie-games are ruining everything good in the world between bouts of "back in my day..."... But yes, there was so very very much potential in Apocalypse. I actually played Apoclypse first, and it was weird, I had a few gripes about it. The limited scientist pool, the lack of ability to bring vehicles into the tactical battles, how everything was stuck in this cramped little city and we couldn't choose where to place our bases... It was amazing just how many of the things that I wanted were already in the preceding games in some form...
Still, nothing else can quite replace the thrill I once got after placing charges under a slum-appartment-complex's supports, watching the thing collapse into a miserable pile of ruins and dead aliens, and then exiting the battle to see the place collapse in the strategic view as well... I don't think that they have demonstrated anywhere near the three-dimensionality required to reproduce Apoclypse's glory. If you can't dig tunnels through buildings, and solid earth. If you can't take flight with your whole team and bombard a region from the far side of the map because you know that there is a brainsucker out there and you are not inclined to go door-to-door looking for it. If you can't fly teams to every entrance, including some that don't exist yet, and breach simultaneously. If you can't gas an alcove and wait outside in the hopes that it faints from the fumes because you really don't want to go in after it... Well, then it just won't be the same game...