What a laughable overreaction. Whoever made the comparisons is seriously telling me that photos of random scenes with characters posing the same way as in various TF2 trailers, means it's a ripoff? Haha. Wow.
When you actually watch the trailer, you'll see that it's very different. There are toy anime girls/robots fighting in a "rats" type of level, in third person. The trailer looks a lot like the first TF2 trailer because it attempts to do the same as that did; to present the different classes in a fighting situation. It's not like the TF2 trailer was original either.
The likeness is either a result of the similar way of presentation (as mentioned), or it's a little homage. The latter does, of course, not mean ripoff in any way.
I'd actually love to play this, if it wasn't for the hideous anime crap that Koreans have to slap onto eveything.