- Frozen screenplay by Jennifer Lee, directed by Chris Buck & Jennifer Lee (Walt Disney Studios)
- Gravity written by Alfonso Cuarón & Jonás Cuarón, directed by Alfonso Cuarón (Esperanto Filmoj; Heyday Films; Warner Bros.)
- The Hunger Games: Catching Fire screenplay by Simon Beaufoy & Michael Arndt, directed by Francis Lawrence (Color Force; Lionsgate)
- Iron Man 3 screenplay by Drew Pearce & Shane Black, directed by Shane Black (Marvel Studios; DMG Entertainment; Paramount Pictures)
- Pacific Rim screenplay by Travis Beacham & Guillermo del Toro, directed by Guillermo del Toro (Legendary Pictures, Warner Bros., Disney Double Dare You)
Frozen is a sweet and wonderfully enjoyable animated fantasy, but as a fantasy work it doesn't really do anything exceptionally new and insightful. The same goes for Iron Man 3, which was my favourite of the three Iron Man movies yet still doesn't feel like a worthy winner. Pacific Rim is a dreadful movie with a real chance of taking home a trophy, since it brings with it significant fan cache via Guillermo Del Toro.
That leaves The Hunger Games: Catching Fire, a solid adaptation of a great novel, that juggles a number of influences pretty well. Its first half is a bit of a slog to get through, but is still worthy nonetheless. This is what gets my vote this year: Gravity is better, but I simply don't think it should qualify for the Hugo.
As for films that unfairly missed out on the ballot, that's probably going to depend on personal taste. Most major SF films of the year received mixed responses at best: films like Elysium, Man of Steel and Oblivion. It's arguable whether Thor: The Dark World deserved a slot - certainly it's worlds better than Pacific Rim, but arguable whether it's better than Iron Man 3, for example. World War Z is another film that sits in that 'almost good enough' area.
Bong Joon-ho's Snowpiercer certainly seems to be the best reviewed SF film of 2013, although I strongly suspect the bulk of Hugo voters live in countries (the USA, Australia, the UK) where it hasn't yet been released. It will be interesting to see if it makes it onto next year's ballot.