Heaven and Earth takes everything that worked from the original series and builds on it. There is a stronger thematic structure and a more focused plot. The story picks up two years after the end of the main series and while it doesn't take full advantage of this change to grow the characters, it still feels like they have settled into a new status quo. That said Heaven and Earth doesn't bother to properly reintroduce the returning characters. If you haven't seen the original series then this show won't make any sense. It doesn't bother re-explaining anything, from Fafners to Festums to Mirs. It's allassuming you're already familiar with these concepts.

The animation was a massive step up from the original series. The fights are incredibly dynamic and fluid. The overall quality massively improves upon everything. This movie still holds up today. None of the CG feels dated (if you were even able to spot it). That said it still has the same issue from the main series where all the character designs look very similar. That combined with the introduction of a few new characters and further focus on some lesser side characters from the original series meant there were a lot of new (but similar) faces to differentiate from.

The characters were good, but nothing incredible. However the standout here was Kurusu, the new addition. His personal struggle is the heart of the movie, and it's well tied in to the themes and concepts the film focused on. A lot of the side characters had multiple separate arcs that arguably shouldn't have worked, but they were all tied together through the main theme of the cost of war, and it helped to paint the picture of war being a grand but ultimately futile struggle with a terrible toll - something that may not have had the same impact if it had focused on only a few main characters.

Overall I'd say this is a must watch if you have seen the original series. If you haven't then this is hard to recommend. It comes with the price tag of having to watch through over a dozen episodes of mediocre garbage in the original series to get to this. However if the rest of the franchise continues to be this consistent it might just be worth it.