This quite possibly is the pinnacle of fighting games.
The graphics and animations are incredible. The new characters are fantastic. All the old characters are similar enough to their original design and play style, but radically updated none the less. Characters that were unplayable in SSF II (meaning-- they were not worth using because they sucked, like Zangief, and the boss characters) are just as well-developed as Ken and Ryu. The roster is enormous, but not one character seems cheated in terms of development. Every character is unique and legitimate.
Playing online is ridiculous-- I just don't stand a chance. Half the time I don't even understand what's happening. But, this is a testament to the skill required to play the game. This ain't no button masher. You really have to know what you're doing or you will lose. The better player wins every match; there are no lucky wins in SSFIV arcade.
The combo system, focus attacks, focus cancels, set ups, etc. are enormously complicated. I think that once you reach a certain age, your ability to understand the subtleties of video games fades into oblivion, forever replaced by the protocols of adult responsibilities and politics. It's just like learning a new language-- up until a certain age, you can learn a language with minimal effort, but there after, it takes years of study. So it is with SSFIV arcade.
My only criticisms of the are these: First, the challenges seem to be impossible for a mere mortal. The game provides a series of challenges to be completed by each character that consist of performing various moves and combos that test the upward boundaries of your digital dexterity. I suppose somewhere in the world, there are 12 and 13 year olds who can pull these off. But, I can't, and I never will. Second, I wish there was a way of hosting a lobby in which you could restrict certain characters; maybe an option of restricting the use of up to four or five characters. It seems like every match I play online is against Ryu, Ken, or Akuma. I'm tired of playing against these characters. Hey guys, there's like 40 characters on the roster, pick someone else. BORING! But that's not really a criticism of the game, rather a criticism of the player. In this case, I hate the player not the game. hahahah.