Eternal begins where Beginnings ended, narrating the story of the final four episodes of the Puella Magi Madoka Magica series. And that's pretty much everything it does.
Sure, the visuals are upgraded (just by sake of a higher budget, not at all changing in style). The soundtrack is more or less the same. The plot, the dialogues, even a whole lot of scenes and direction are perfectly identical to the series. I only remember a single half-scene that was added, though I'm sure there must be more; after all, the movie is something like fifteen minutes longer than the four episodes. But still, it doesn't bring anything new to the table, and it is by that somewhat flawed.
The first movie gave the first eight episodes a similar treatment. However, those eight episodes narrated a continuous story, so that movie could basically just play the respective episodes back to back with some minor adjustments for pace. The second movie doesn't have that option because episode ten tells a character's backstory. It still pretty much just plays the respective episodes back to back, with a somewhat jarring cut to signify the time skip. IMHO it became fairly obvious at that point that the episodic series is simply the more natural medium to narrate Madoka Magica; there is very little reason for these two movies to exist at all.
That being said, the movie duology of Beginnings and Eternal is perfectly fine, there just is very little reason to watch both the show and the movies. Potential viewers now get the fine choice of having to decide between the few extra scenes of the series or the prettier visuals of the duology, and I just don't get what the point of that is. As good the these two movies are, their existence is pretty much unjustified. They're still very good, though, I guess.
