Omo addresses the question if parts of ef form a sequence or something else:
As the second season, ef - a tale of melodies, comes to an end, it becomes increasingly clear to me that the two seasons were planned in conjunction. [...]
It also makes me wonder if I can truly appreciate the core content to the show without experiencing the entire package – both the games and the two season of anime. The stories as I hear from the game suggest that the anime are indeed complementary, rather than adaptive. And likewise, a tale of melodies complements a tale of memories; they are only sequel by definition, not by function, much like the two games are parts of a whole.
I'm still not planning on watching the ef ~melo~, primarity out of concern that it would damage the memories of its predecessor, sequel or not. Seriously, Kuze+Mizuki? More like ef ~sacriledge~!
BTW, Omo's shoutout blurb managed to represent my position exactly backwards, it looks like. If I wanted "more of the same", I would look forward for a sequel, deshou?