And even the lack of backstory makes him scarier..... ok some information would have been nice.... and a little more dialogue.
Also like some one in EQD said. Nightmare Moon has the best back story, Discord has the personality, Chrysalis has the motivation, and Sombra has the best presence.
Also because I treated him more as a plot device while I was watching the episode.
1.) Have him speak, even if it has to be only one line
2.) Make his voice suit the character, not a high-pitched voice like Snips, or worse, Majin Buu
3.) KILL HIM OFF AT THE END (we need at least one official villain death to measure up to G1, Chrysalis was debatable so she can't be counted "official")
That being said, I was 100% satisfied with The Crystal Empire. King Sombra was an overachiever IMO because he was darker than Chrysalis, which is saying something. Though parts of the episode seemed slower, whenever Sombra did appear the scenes were epic and he was quite menacing, especially with his evil Andross-style laugh during the scene where he regenerates his horn. Also, one of the most epic Chrysalis-free moments of the show is when he tries to kill Spike with that dark crystal, and we see how psychotic he is when he licks his lips at the thought of skewering a baby dragon. Although he didn't speak much, atleast he had any lines at all, and that highlights his resemblance to Sauron, we needed a MLP counterpart to Sauron because Lord of the Rings is the most commonly referenced show in MLP and we already had three Gollum counterparts (four if you count Twilight in Lesson Zero). And unlike Sauron, he actually tries to do something when his doom was near, and regains physical form. And his death scene was one of the most unique and spectacular I've ever seen, and Meghan confirmed it too. (I know some were disappointed by it, but more were disappointed when Discord turned good, myself not included)
And it's been said in the Elements of Harmony book, Sombra was underestimated by many as a villain. If given the chance, he'd have done some real damage. Why didn't he do more than he did? Because if he could have, he'd have probably killed the Mane 6, Princess Cadance, Shining Armor, and definitely Spike. Well, maybe he'd see Applejack and Pinkie Pie as slaves with the crystal ponies, but any pegasus, unicorn, or alicorn he'd probably want to eliminate then and there. (Also of note, what happened to the pony who ruled the Crystal Empire before Sombra took it over? No previous ruler was seen and the empire was given to Cadance and Shining Armor after Sombra's death)
Overall, second favorite villain next to Chrysalis. (Discord's position was third even before he turned good, but I still like him)
I honestly would like for Sombra to return to face the Mane Six once again. Here's my opinions as far as villains go:
Nightmare Moon makes me sorry for her the most
Discord is the most entertaining and the most powerful
Chrysalis is the most deceitful, but the least powerful
Sombra is the most malicious and the most complex
Why? Because he is King motherbucking Sombra! Lord of Shadows! Emperor of the crystal ponies!
Seriously now, having a villain that does not talk is a bold move.
If a Villain talks, that means you can reason with him or outsmart him. The episode makes it clear there is no reasoning with Sombra. When he gets into the city, all is lost.