I'm copy/pasting a post made by Darth Spell on the Shoddy Battle forums. Shoddy just recently held a tournament where Deoxys-E was unbanned and this is what he had to say about it after playing in the tourney:
"When I heard Deoxys-e was going to be legal, I made all attempts to be sure that I'd be prepared for it...but when I finally found the Deoxys-e, it didn't last two seconds against my lead Yanmega anyway. Yes, he has enough speed to outrun Jolly Scarfchomp and OHKO with Ice Beam, but isn't that a good thing? Yes, he has a massive movepool, but does he really have the stats to use them? Against stall teams, normally vulnerable to mixed sweepers, yes. Anything else? No. However I mean, Superpower takes down Blissey, Shadow Ball takes out Cresselia, Thunderbolt takes out Skarmory and Ice Beam takes out Gliscor and Hippowdon. Aren't those good things? The most overused Pokemon in the game are destroyed by this "Uber", and yet the likes of Ludicolo, Dugtrio and Spiritomb fare well against him. Azumarril, Arcanine and Ambipom can strike in and KO first. Drapion's typing and Dark status makes it great for Night Slashing it into a grave. Scizor comes in on Ice Beam and Psychic and Swords Dances while the opponent expects X-Scizzor - if he stays in, kill it with Quick Attack. Steelix resists all of his mainstream attacks minus Superpower, which will just bounce off his 500+ defense anyway. Sash Cacturne and Absol can start to see more play thanks to Swords Dance / Sucker Punch. Jirachi has virtually nothing to worry about and can setup Calm Mind on it if its bulky, give it paralysis if it has Thunder or hurt it immensely and escape if it has U-Turn. Anything with Thunder Wave turns this thing into dead weight. Bronzong and Dusknoir, who are slowly loosing popularity, turn many variants useless as well. The game will become even more diverse, more strategic, turn alot of known facts into guessing games - as the "whores" lose usefulness, the underdogs will rise. The game will even out, meta will merge, and interest in the game will kindle faster. And if I'm wrong, its much easier to ban a Pokemon than to unban it...just look at the Manaphy case. Deoxys deserves a chance...the game deserves to see what it could be with a mixed threat other than Infernape on the table. The game isn't changing radically because of this, but its a breath of fresh air.
So the meta is shattered and diversity reigns supreme. Does that mean that the rest of the Pokemon community besides the incredible overused rapists of Garchomp and Blissey will lose effectiveness? No. Just because an attack is Super Effective doesn't mean its going to KO. In fact, in all my battles using Deoxys-e, he hasn't been even close to KOing a single Pokemon. Not to mention that his item of choice, Life Orb, drains his pitiful health stat to even more deperssing numbers. While Deoxys-e comes in to shatter Hippowdon, I wouldn't swap my hippo. Ice Beam does alot of damage, but definitely doesn't kill it. Then I'll be free to kill it with Earthquake after I absorb the attack. Superpower doesn't KO OU Blissey, unlike Uber Blissey, so she can still get in Thunder Wave, Softboiled, Wish or a finishing Seismic Toss or Ice Beam. Is Tyranitar scared by Superpower? No. Crunch ensures Deoxys-e won't come in on the switch, and Tyraniboah can just hide behind a Substitute as it comes in to finish it with either Dark Pulse or the aforementioned Crunch. Togekiss does extremely well against Deoxys if it doesn't predict a Roost, but Thunder Wave will cripple it, and Air Slash will seal the deal anyway. Weavile might not like Superpower as well, but Deoxys-e hates Ice Shard and Pursuit just as much. Bullet Punch Metagross kills Deoxys-e before it gets a chance to move - let's not forget that it also has the deadly Super-Effective Pursuit as well! Choice Scarf Gengar can hurt it with Shadow Ball if it isn't facing something with an exhausting about of speed. Swampert absorbs an attack and kills it with Earthquake - especially Special Defense Swampert. Shadow Ball Deoxys-e takes awhile to take down Cresselia with Shadow Ball, and it can Thunder Wave it in the meantime or Calm Mind as it hacks away and Rest the damage off. Lucario comes in on alot and uses either Swords Dance / Extremespeed, Crunch, Dark Pulse or Shadow Ball to end its happy day. Special Defense Milotic and Calm Mind Suicune laugh at his attacks (the ladder needs a turn or two of setup to be comfortable) and either OHKO or 2HKO with Surf. Deoxys-e will find itself in heavy competition with itself - who can be the fastest in case of a mirror match. This of course results in weaker and weaker Deoxys-e attacks, which makes it even easier for all the other Pokemon to defend against it and kill it in no time flat. Speed isn't everything, apparently."