Pokken is actually pretty good and I think it's worth the buy. Not sure what they've done to it since the first few months of release but it's kinda like actual pokemon
Super Meta Dominate
Tekken isn't hard to pick up, and they have some moderate pokemon (Pikachu, Charizard, etc). I wouldn't say it's too similar to stadium though. It's like any fighting game you get, where it's pretty good for a bit but then it gets stale. They add content really slow iirc and I'm not sure if the speculated dlc pokemon they were adding were ever actually even implemented.
Good game overall, especially if you aren't going to buy it yourself. Really really good party game, it's a lighter tone than normal tekken and isn't too insanely hard for a first time player to pick up on.