I'll offer my two cents, with the warning that it is me, and if you don't know me I am basically watching from the sidelines, plus while I've been with the English release of Pokemon since the beginning, I've had multiple hiatuses and my last one meant I missed almost all of the SP format.
Still, my experience has taught me never to underestimate subgroups within cards. Pokemon SP had so many options going for it. Head to head, Raikou is bigger, hits harder, is a Basic, and can be run at four per deck if desired; the only downside is the two Prize penalty with the anticipated card pool. Garchomp was a Level-Up card (a pseudo-Stage 1 that shares slots with the Basic is "levels up" from), smaller, and didn't hit as hard, but it enjoyed all the SP tricks. Yeah that meant it was vulnerable to some counters that don't currently exist for Pokemon EX, but the whole package that was Pokemon SP and the formats they were available in means I don't expect Raikou EX to have the same impact.
Having just seen this card (I've been a bit distracted by life
) my first impression is that this will be played and function as a dangerous sniper, but anything more is pure conjecture. Formats where past snipers have been potent didn't have Pokemon Catcher. Similar cards? Sure, but not something as good as Pokemon Catcher. Head to head Raikou EX is better, but factoring in everything Garchomp LvX had more going for it, such as more promising sniping targets to OHKO.
Raikou EX will be at least a signature TecH card for Eelektrik decks. Slam into Trainer denial? Laugh and snipe the Bench they want to protect. Raikou EX isn't the only sniper, though, and Zapdos has three things going for it:
1) Not a Pokemon EX (120 HP is still good and it won't cost you two Prizes)
2) Hits only for 50 but doesn't shed all its :lightning: Energy and can make use of DCE for a first turn snipe!
3) If you "have" to hit an Active Pokemon hard, Zapdos has at least a shot at it. A "bad" big attack can still be a good thing.
4) Fighting Resistance instead of Weakness; very important for a deck that is almost all Fighting Weak.
Zapdos is not better than Raikou EX, but I think its features make the two a pair: Raikou
needs that good set-up to do more than stall. Neither can attack first turn without help, but with just a single :lightning: and a Double Colorless Energy Zapdos is ready to snipe second turn. Raikou needs yet another turn and after attacking under such circumstances may shed all its energy if you don't have an off-type Energy attached to cover the :colorless: cost of its attack.
If we want to see a general Big Bad Basic Pokemon sniper, it will be Zapdos: most such decks already make use of Double Colorless Energy and Prism Energy (at least if that's out yet - like I said I've been busy and sounds like I missed the Pre-releases the way people talk). It isn't happy to require two special Energy, but for a 120 HP basic that snipes for 50 points of damage and can make a big desperation attack before being KOed for one extra Energy of any Type, it is just fine.
tl;dr: With what we know right now, I assume Mewtwo EX will be the more common "big Pokemon EX attacker" whether on or off-type for the deck, the other big Basic attackers will still be around and swinging, and Zapdos is the splashed in TecH sniper. For actual :lightning: decks, Raikou EX will at least be in as a TecH copy, bumping a Zapdos. Could be
more than that, though.