Quoted By:
The only thing that really disappointed me about gen VI was that legendaries were so thin on the ground.
I enjoy the thrill of going on the mini quest to find them and battling /catching a powerful pokemon, and it gives you a sense of achievement if you are able to catch the trio as well, this time all we got was one new optional legendary that they didn't even try to add any in game folklore about with a fairly straightforward quest to catch.
No new trio, no mystery or puzzle to solve like you had with the regis (a high point in legendary questing if ever there was one), just a Mewtwo, again, and ONE of the birds, again. If they were going to reuse legendaries why not ones that you might not have like darkrei or arceus, rather than ones that, if you have been trading up through the generations as you were supposed to you would have at least twice already!
Only being able to catch one of the three birds left you feeling a bit short changed too.
I suspect they just ran out of time and couldn't put new legendaries they'd planned in as there are places on the map that hint at something epic but are completely empty like that cave at the bottom of the waterfall where they just shoved an 'ite' in it or the sea beast cave where you encounter your game's bird which has bugger all to do with the sea or beasts.