When you take a very cliched genred and try to make something original out of it there are 3 possible outcomes. It can turn into a memorable masterpiece. It can turn into something so weird only the angsty kids would watch it while prouldy saying it's "alternative". Or, and this is the outcome in this show case, it can look like cliche anime that is trying a bit too hard.
This show is a typical light lovecom to the core. We have childhood friends, love rivarly, oblivious-energetic chara, intelligent tsundere chara - basically completely typical. So how can a show gain the edge to shine a bit brighter than all the other shounen love polygons? By getting a not overused theme (astronomy) and mixing in some astronomy knowledge. And everything would be perfect if not the tiny little detail - they couldn't get the right proportions. Astronomy that should be a spice suddenly takes almost the same amount of screen time as the "main dish" romance. And so we have characters lecturing each other about the wonders of the stas, then showing the starry sky, then marking the constellation on said sky, then gasping a the beaty of those constellation, followed by another lecture about them and after all that finally we got some emotional punchline (usually only as a character thought) like "A, watching the stars together feels so good".
Since (thx to neverending astronomy lectures) plot was moving at the turtle pace, the only thing that kept the show alive were likeable characters. They weren't really complex, or really original but they created this fuzzy atmosphere of friendship that makes lovecoms such an enjoyabl genre. There was a bit of low lvl drama, a bit of humour, some character growth - prety much the usual and predictable stuff.
The animation and the sound were both average - nothing to complain, but nothing to be amazed about either.
Sora no manimani isn't top of it's genre. It's too slow and filled with too much story unrelevant information, but it still can be enjoyable. Don't expect anything amazing though.