We all liked the first film more. Farmageddon was okay, but adding the sci-fi trappings (and the pink and purple colour scheme) didn't really fit the setting so well--- which could have made for a fun film, but ultimately I felt it was way too reminiscent of ET, and not enough of its own thing. Fun, but unmemorable. Also, the design of the aliens was, I thought, quite uninspired.
What I wrote to Rand after our double-bill of both Shauns last week:
Quick take: as good as the first, but where it lacked in surprise and originality it made up for in scale. I think I prefer the first, for the continuous invention, though Farmageddon had more size, even if a lot of the situations seemed to be borrowed from other films (and not just the obvious joke references).
Even more interested to see DreamWorks' Home now, even though my heart kind of sinks whenever I think about watching it...!