Actually Beat 'em Up is a different genre with roots in things like Final Fight and Streets of Rage, modern takes on it are things like Dynasty Warriors.
Personally though fighting games are my favourite genre, although MK isn't my favourite among them. They're a genre which is quite difficult to get into, but if you throw time into it they can be incredibly rewarding especially when two skilled opponents go against each other.
They aren't just mash buttons and win(well perhaps if your only playing against people new to them). You constantly need to think about spacing, know your opponents moveset and guess what they will go for, you need to grasp a variety of concepts like frame cancelling, negative edge and how to manipulate wall and floor bounce etc. Once you understand them you need to know when to use them often with no time to think about it. There are a lot of awesome things about the genre, but if you play SP only then yeah I can see it getting dull.
Some of the best gaming experiences I have had are from fighting games, they get incredibly tense when both players have a sliver of health left and the clock is ticking down.
The new characters have grown on me. I am loving the arenas so far and the anti getting stuck in the corner is fantastic
The new styles of fighting are a nice idea I hope they pan out nicely.
Just read one of the new playable characters will be the daughter of Johnny Cage and Sonya Blade, Cassie Cage. Don't know if there is much truth in this, but I are disappoint. Sonya, you can do better...