Well, I didn't think the acting was the worst, it did what it needed to. Not much to write home about, but some noteworthy moments, like the bit going back to Rinko Kikuchis' characters' traumatic past, or one last ride early on.
Or, a last goodbye between family late on. Maybe not necessarily acting, but it didn't ruin the moments for me.
And yeah, I saw the first film for Giant Robots Vs Giant Monsters, but I'll be seeing the sequel for an expanded universe, or world tales continued.