I know I've thought "those aren't Pokemon" for a handful of designs every generation starting with Gold/Silver, and I know I've always gotten used to everything I've thought that about... But even considering my history, I still don't think I can get over a crazy baby covered in ectoplasm in the shape of Gligar, or a thing in a black Christmas-tree-looking dress. The black and red thing just barely gets by looking kind of like Heatran. (I admit I hated Heatran at first too.)
Hope I'm wrong again. Kind of strange that only now they're getting to new Pokemon designs I don't like, since I thought the crocodile, Fire ape, zebra, and two out of three starters were really cool in the same way I always liked Mareep and Lanturn.
I actually see more competitive potential in triple battles than double battles just because having three Pokemon on the field is enough to allow for one of them to be a dedicated gimmick set like Smeargle with Imprison/Explosion/Discharge/Spore, or a starting trio of Intimidate Pokemon, etc. (Even if Gyarados and Salamence don't get any new and better Intimidate partner than Arcanine, that would still be okay for stopping exploding Metagross.) I don't know, obviously better stuff would come up than what I can think of in a couple seconds without knowing the new moves or Pokemon, but I'm just tossing it out there. I wouldn't play competitive triples anyway.
...but what I do definitely think is that single-player can really see a gain from this if they incorporate triple battles (and doubles, for that matter) into the wild, and not just for a couple dungeons like in fourth gen. Fighting all three stages of an evolution line simultaneously would be cool, or just a flock of birds or pack of dogs, so that instead of running into three of the new birds in a row, you run into three of them at once. And if the encounter rate was cut by 65-75% but they added that chance of double and triple battles to compensate on the dungeon run endurance factor, maybe I wouldn't have to use Repels all the time throughout the entire game.