Honestly I've thought the Ice Age series has been on a steady decline after the first three, but this one just took a nose dive.
First, in the beginning we have Ellie summing up their previous adventures. Cool, but several key characters (Shira, that girl who got with Sid, Sid's grandma, heck even her own daughter Peaches) went unmentioned.
Second, the new voice actors are pretty obvious and not good at all. It distracted me everytime a character spoke.
Third, the story focused on some of the worst characters from the movies (Crash and Eddie), and even made Buck bland and uninsteresting.
I was only a few minutes in when I realized I hated this movie. Plot had weird pacing, animation was static, and the villian was poorly designed and I couldn't take him seriously. Some movies I can enjoy even if I don't think their good movies, but this movie wasn't enjoyable or good. It feels like a bad fanfiction without ever considering the fans of the series aside from making Buck a main character (but they even messed that up, as I mentioned).