You can pretty much tell what this is by the title. Everyone always regards Arkham City and Arkham Asylum as the greatest superhero games ever. While they were amazing, they are not as good as Ultimate Alliance. Sure, MUA may not be the best graphics ever in a game, but it's still an amazing game. Here are reasons why it is better than Arkham City and the greatest superhero game of all time.
The scope of the game is gigantic. It has simple places like the Helicarrier or the Omega Base to more complex areas like Murderworld or Atlantis, to magical places like Mephisto's Realm and Asgard, to cosmic themed areas like the Skull Homeworld and the Shi'ar empire. and that's not even all of it. Arkham City does have a lot to cover, but once you go through enough of it, it just gets old, boring, and frustrating.
Ultimate Alliance has a HUGE roster of villains. From Dr. Doom to Galactus to Loki to Enchantress to Mephisto to Attuma to Mandarin to MODOK, etc. It's just amazing. Yes, Arkham City did have an enormous roster of villains. But there were just too many, leaving some to do nothing. Two-Face is a prime example of that. He is officially in the game, but what does he do other than have more henchmen for you to face? Then there are villains who are reduced to side missions or cameos. Black Mask deserves better than that. Ultimate Alliance may have A LOT of villains (possibly more than Arkham City), though it's not too much. No one had to be reduced to a cameo or anything. Every villain got their fair time in the spotlight.
Does this even have to be explained? The heroes in the game are even more impressive than the villains. With Captain America, Spider-Man, Thor, Wolverine, Iron Man, Storm, Daredevil, Ghost Rider, Iceman, Dr. Strange, Black Panther, Nick Fury, Deadpool, Moon Knight, etc., you can have whoever you like on your team. And you don't have to buy the overpriced DLC in Arkham City. Really, it would of been that hard to throw in at least one mission with Robin that wasn't DLC? MUA has the perfect roster of heroes to go against the perfect roster of villains.
The gameplay in Arkham City is AMAZING, I admit. You could easily entertain yourself for hours by just going around and beating people up (well, for some time at least. More on that later) But there's too much. There's just so much to do you loose track. You have no idea how long it took me to learn and remember how to divebomb. In MUA, there's a lot to do, but it's simple. Easy to remember, equip, etc. Plus they don't try and overdo it.
After You Beat The Game
I admit, I had extreme fun after beating Arkham City. I did some side missions, found easter eggs, got some riddles and riddler trophies, etc. But it's gotten boring. At this point, it's gotten to the point where your only thoughts are "How the f*ck do I get this f*cking riddler trophy!?!" In MUA, sure, it might still be the same thing. But with the amount of people to choose from, you can have equal fun every time playing it as you did the first time. Plus if you failed a side mission, you can try it again the second time around. You can try and find more simulation discs, etc.
There is no game out there with a more epic story than Ultimate Alliance. Sure, Arkham City was cool, but there was just too much going on. In Ultimate Alliance, the plot is epic, yet simple. Dr. Doom forms the Masters of Evil to try and take over the world, so Nick Fury forms his team to fight the Masters. It's simple, easy to remember, and is cool. Then, as the game progresses, it gets even better. Doom starts by doing simple stuff like attack the Helicarrier, but eventually starts taking us to Mephisto's Realm and Asgard. When it gets to the point where Doom is stealing Odin's power, it's just truly epic. And aside from Doom taking over Earth, there's an even greater threat with his powers destroying the time/space continuum. That's when the Shi'ar (cool plot for that mission) and Galactus come in. Even aside from Doom and the Masters, there are awesome plots when it comes to stuff like Mephisto's Realm. Choosing to save Nightcrawler or Jean Grey. How awesome is that?
In conclusion: Marvel Ultimate Alliance is the greatest superhero game in existence. Sure, Arkham city was cool, though it's not as good as MUA. Ultimate Alliance was better in story, gameplay, villains, etc.