(No spoilers below.)
In my opinion, SAC2 isn't as good as SAC1, but that may be down to the translation in the fan-subs I've seen. I've noticed that fan-subs tend to be more verbose, trying to stick to the original meaning, where the official subs tend to be tighter and while they may miss a nuance or two the whole thing hangs together a little better.
Still, I felt the whole SAC2 storyline wasn't as strong as SAC1 and felt needlessly obscured behind pompous literary references. In a sense, I felt like the writers were saying "ha, not read Hemingway you illiterate caveman?" and that tends to peeve me some, not least of which that I couldn't give a flying crap about how many references a writer can stuff into their writing; I only want to know about this story and these characters, no matter where you drew your source material.
Still, SAC2 assuredly has its moments and the animation is always worth watching and, from what I've seen of the briefly-posted link to the next film it's probably required watching before starting on the film. Some snippets give me the impression it directly follows on from events in SAC2 and, as such, may spoil SAC2 if watched first.