Okay, going to talk about each card spoilered yet:
Gengar Ex:
I'm really happy with Gengar Ex who will work nice with Trevenant/Gothitelle (Gothitelle having the nice 0 retreat cost with the new energy).
Balanced but still something I would think about as a deck.
M-Gengar Ex:
M-Gengar Ex is nice too, works really well with the new stadium and one of the few (maybe the only one yet with Lucario) who I'd consider playble.
But it still depends on the opponents deck, how useful it is. Interessting is, there is no "other costs" disclaimer on the card, like it was on the metronom cards!
Dialga-EX:
Disapointing legendary Ex Pokémon.
You read the first attack and hope the second is really cool but then... Meh! It's a worse Charizard attack. xD
Playing this is not the best idear, especially since Pyroar is so popular.
Aegislash-EX:
Now where talking! It's not a Pokémon you will build a deck around, but you can splash it easily and it will be annoying as h*ll. ; )
The attack is decent too, not too strong but okay.
Zubat/Golbat/Crobat:
What a sneaky ability (*cough* bad joke).
Reminds me of the old, and annoying, Crobat G, back in the day when we had real rotations without reprint sets... : /
This will see play and with the new stadium you can attack for free, which is always something.
Ditto:
A really classic ditto, but with a nice upside, that it got a own attack. But too low on HP to be considered playble.
Dimensional Valley:
Okay, they kinda got their point by printing really strong stadiums. This feels like the era of strong stadiums after we had a strong item cards era (and supporter before that).
We might see 1-2 new decks with old Pokémon added. But don't like the art, a bit too much of a rainbow color, bright theme for psychic. (I know it should be ectoplasm but for me it looks like skittles or smarties : ) )
AZ:
It kinda obvious he got spoilered to promote the hype for the Crobat line and he is a bit stronger than Cassius, since the cards are not gone and you can play the preevolution again and maybe evolve another Pokémon on the bench?
A fixed super scoop up in my eyes and that saw a heck of play back in the days! (Do I sound old by now? xD)
Mystery Energy:
A bit... Disapointing but fair and it's obvious why the (compared to strong energy) low powerlevel. The effect is nice and with a already this strong stadium in the set a powerful support energy would have been too much. This one is a perfect match.
Works nice for Gothithelle.