Personally, I believe it to be the best of the Mortal Kombat three dimensional series. But then, that might be me speaking subjectively.
First of all, the rooster of characters.
Let's parallel between MKDA and MKD. Now, on a personal level, I was never a great fan of most of the characters in Deadly Alliance, especially ones that I felt had become less delivering of impact through the transaction onto 3D. Characters like Jax and Kung Lao, didn't really play like they did in the old days. Most of the previous characters came back looking, in my opinion, really stupid, like Jax. The new characters, like Hso Hao, Nitara, Mavado, really didn't impress me, and were kinda bland. Characters like Scorpion and Raiden though, remained fairly faithful to their original vibes. But Deception, brought back alot of characters from the past, like Baraka, Nightwolf, Mileena, Ermac, Jade, Sindel, and made them work. Sindel, especially, kept up the vibe she had from the 2D era. Baraka, I felt, was taken as he was and IMPROVED alot, Mileena seemed more smooth and fluid etc. Along with a few kombat zones and music, it felt as if it brought more of a MKT feel back to the mix BUT YET still moving forward.
We get characters, new characters, like Shujinko, Kobra and Kira, that weren't just brand new characters with totally new movesets, but rather Scrappy versions of previous characters, namely Kung Lao, Sonya, Cage and Kano. Then you got characters like Darrius, that were still there to give the ethnic balance. I for one, became sick and tired at this point of "Earthrealm warriors" just imposing their safety ideals. It's good and all, but it was overdone. I became sick and tired of Jax, Sonya and Cage, ironically the iconic favorites.
Deadly Alliance claimed to be dark and edgy, but really wasn't as much as it appeared. If by dark, you mean gloomy and dull, maybe. But the Earthrealm good guy" warriors were still alive, in sufficient numbers, doing the same old thing they always do. Before Deception, they were (in theory) killed off, which was great, because now the series could focus on a new light, an ACTUAL edgier dark feel.
Raiden, the old obi-wan of the good guys, was now a corrupt wrathful being, that cared not for mortals, only the perseverance of the Earthrealm he considered his own.
Shao Kahn, considered the scary big-bad for the majority of the time, was actually a force trying to claim back something from the TRUE big bad.
Liu Kang, former "ace" or "hero", becomes a chaotic wandering zombie.
Of the five warriors that ARE from Earthrealm, THREE of them are evil chaotic bastards from the Black Dragon (where as previously, we had 1 per game). The other 2 were good guys, but one was a moody loner, and the other was a mysterious loner that attempted to taint his soul. Such a contrast to several Earthrealm warriors teaming up to take on an evil, there was no real "good guy" team now. Now THAT is dark and edgy. MKDA didn't do that.
The game was not about good vs evil, it was about chaos vs order. That's what made it dark and edgy, as opposed to just giving it gloomy visual effects.
It's alignments were ambiguous, where as before they were clear, especially with the new inclusion of chaos vs order. Characters like Ashrah, for example, was a DEMON who was trying to ascend to goodness. We got alot more selfish neutrals like Darrius, who would commit malicious deeds, but were not aligned to the big bads (but rather doing things for themselves), and true neutrals like Dairou, who aided whoever paid them. I felt this really gave the series and edge.
The rise of Onaga gave us a new boss to beat, rather than MKDA's repeating of Quan Chi and Shang Tsung (although they did give us Moloch as a sub boss). It was interesting to have the agile flexible characters as the sub-boss, and the inhuman monster as the final boss, which no other game in the series has ever done.
The gameplay was much better. Characters seemed more attractive, and they reintroduced the second fatality option, as well as the Hari-Kiri suicide moves. Death traps as well, returned once more. The konquest mode, was greatly improved, rather than effectively just being a training mode (although it still included training). The krypt didn't feature dozens of empty koffins to annoy you. The chess mode, once you get the hang of it, is an excellent addition. I personally felt it was superior.
Compared to Armageddon? Well, as mentioned, it's a debate on wether you want less characters with more focus, individuality, and more than one unarmed fighting style... or several characters from all the game, with less individuality, one unarmed fighting style, and many repetitions of generic features.. Depth or length, I guess, entirely up to a person's general desires. The konquest mode is alot less detailed and advanced as Armageddon, but MUCH larger and more playable. I feel that what Deception offers is manageable yet delivers a sufficient impact.
And I'm a little bias because the set up it gives, contains most of my favorites of the 3D era, and even introduces my favorite.
I feel so alone, gonna end up a Big ole pile of them bones.
