bread and roses and spiders
120 damage is not really that strong at all, actually. We're in a very OHKO-centric format right now, meaning 120 damage really isn't what it used to be, and an attack cost of 4 really hurts (remember, this is the primary reason why the theoretically super-threatening M Tyranitar-EX never got past tier 3, even with Yveltal support and plenty of ways to make Destroyer King strong enough to OHKO the entire format). Sure, you might be able to pay for that with two DCEs, but you will not be killing much of note without at least 3 Water Energy attached (two with bat support) because you're essentially forced to run Gyarados Spirit Link, and you're also massive hammer/Xerosic bait at that point. The only EX you can handle like that in Standard is Shaymin, and the non-EX attackers in this format can either shut M Gyarados down completely (Regice) or just set up and start smacking things so fast that it won't be able to keep up on an even prize trade (think Vespiquen and the Hawlucha/Mienshao combo) What this means is that it's incredibly difficult to get M Gyarados-EX off the ground, and the base form relies on coin flips to set up unless you have heavy support (and also damages your own mons when you try to attack, making your benched Shaymin-EX even bigger Lysandre bait than before).This card is pretty good. Gyarados EX first attack should at least get you 1 energy. Something like "search your deck for one energy and attack it to this card, then flip a coin. For each heads, search your deck for an energy and attack it"
Not sure why people are saying the card sucks. 120+ damage is very strong.
Now, it's entirely possible that we'll have Palkia-EX and Golduck BREAK to work with in this set, which might make M-Gyarados semi-usable where it wasn't before (the base form is still extremely lackluster), but at that point you have to ask yourself why you're bothering to use that instead of Primal Kyogre, which has a similar damage output with the ability to smack around your opponents' Benched EX mons as well and sets up faster due to Alpha Growth. And if this is being run in an Archie's deck in Expanded, Keldeo-EX is better suited to that anyway. I'm not gonna pass final judgment until we see the rest of the set, but unless something pretty drastic is waiting to be revealed, neither of these cards is going to see serious competitive play.