A few observations I've made...
While it bothers me that there's no in-universe explanation why there're no male gems - well, as long as you don't count the Russian dub - having one would probably cause some unfortunate implications. I'd still like an officially male gem though.
At first I assumed Opal being much smaller than Sugilite and Sardonyx was simply a stylistic choice. But it makes sence when you realise Opal is only a two-gem fusion while the others are three-gem fusions.
The songs are really good. Normally I find songs in cartoons intrusive, but I don't mind them here. The main cast can all carry a tune.
On the same note, waiting 'til the season finale to give Garnet a song was a great choice. 'Stronger Than You' was worth the wait.
Amethyst 'shifting into Rose was a really fucked up thing to do. Worse than most of what Pearl has done thus far.
Speaking of Pearl, WTF is wrong with her? Taking Steven into space in a hammered together spacecraft, lashing out at Steven over his mother not being 100% honest with her, training a human child with no prior combat experience to act as a knight to a half-gem who by this point is capable of defending himself. And all of this is BEFORE the Sardonyx incident. I don't want to hate Pearl, 'cause she has a lot of redeeming qualities. But the writers are making it hard not to.
The theory that Jasper is a fusion is one I could easily dismiss... If it weren't for the fact that Malachalite is much larger than any two-gem fusion so far. This could simply be to make her a more credible threat, but I dunno...
I like Jasper's weapon. How much of a sadist do you have to be to have your main method of attack be HEADBUTTING YOUR OPPONENTS IN THE FACE?!
I've seen a lot of fanart that assumes Lapis, Peridot and Jasper will side with the Crystal Gems against Homeworld. I can't see it. I could maybe see other gems joining the ranks of the CGs, but to have LPJ on-side by the end of season two seems unlikely to me.
Greg looks like he aged at least a decade between meeting Rose and her being pregnant with Steven. ...And then not a day since then and the present. Cartoon logic, I guess.
While it will probably never come up, I like to think a fusion between Steven and Pearl would result in a genderbent Rainbow Quartz.
Rebecca Sugar has confirmed there were other Crystal Gems besides Rose, Pearl, Ruby, Sapphire and Amethyst. Sounds like a good way to feature other characters without crowding the cast. Again, might not come to anything, but you never know...
