Now that's pretty cool! EXs are indeed going to return, and Mewtwo EX is pretty good for an EX. 170 HP makes it really hard to KO, especially with Eviolite and Defender. As an attacker, he's also pretty good. The first attack is what gives the most potential, as it could potentially be hitting for huge damage due to the fact that most Pokemon in this format (other than Yanmega) need about 3 energies to attack usually. Psycho Drive is also pretty decent too. So far, it looks like Mewtwo EX will definitely see play when it comes out.
As for that promo Stadium, it is not really impressive (but the artwork is really cool in that it looks quite glittery). Speed Stadium is far better than Battle City because you could draw more cards using it. Battle City lets you draw one, so right there, it isn't that much of a good card, and I can expect it to probably be a good card for collecting only.
Well, I can't wait to hear what Reshiram EX, Zekrom EX, and Kyurem EX do. Hopefully, they'll be just as good as Mewtwo EX. I also hope that normal Pokemon can also be EXs. I'm kind of getting tired that only legendary Pokemon get all the cool stuff these days (evident because of Pokemon Legends and Full Art Cards, as ONLY the legendary Pokemon have been able to appear as such via these cards).