The little tag line which appears just for an instant at the end of the GW1 trailer should state it all;
"The Weird Just Got Started"
That's what drew me to the original Tower Defense game and it's what brought me into Garden Warfare.
Regardless of what characters and such wind up in any prospective GW3 I think the setting is most important. With GW1 it was actually pretty weird and the setting really gave off the desirable vibe of the Zombies emerging from the edges of suburbia, crawling out of the graveyards, the mountains and the sewers, and assaulting the towns with only the Plants to hold them back. It was weird and the settings and maps helped promote that.
GW2 lost a lot of that feeling when they embraced the whole Time Travel motif which featured heavily in PvZ2. The Herbal Assault Zomburbia and Zombopolis maps have some of that same feeling from the Plant side and The Great White North for the Zombies but I didn't get that same feeling from the other maps. That and a subtle difference in the art style for the game changed the way it feels when you play it. In the GW1 maps the terrain often actually evolved as you fought your way to the goal at the end and that helped enhance the feeling that you were actually going somewhere; you don't see that very much at all in the GW2 maps.
Regardless of where the franchise goes from here I'm hoping to get that same environmental "feel" back from GW1 where there is a subtle story being told
