Halo 4: Forward Unto Dawn, despite the name, doesn't really align with the actual game's plot line very much. Cortana does act strangely near the start of the game, but how she relates in the movie is being stranded on a ship, which is similar to the end of Halo 4, the game. Use of the concept "Deus ex machina" or "God from machine" was obviously used as an upsetting part of the movie. This gave it no plot to follow by other than train, get killed, retreat.
Summary
There could be a better story line
The deaths we're all too sudden
References:
“Deus Ex Machina.” Deus Ex Machina, Merriam Webster, www.merriam-webster.com/dictionary/deus ex machina.
Halo 4: Forward Unto Dawn, www.imdb.com/title/tt2262308/.
Schedeen, Jesse. Halo 4: Forrward Unto Dawn - Season Review, www.ign.com/articles/2012/11/11/halo-4-forward-unto-dawn-season-review.