So I just finished the game.... And it was amazing. This game is the first game i was busy with rebuilding teams and i liked it a lot (btw final Giovanni battle was disguisting, for me the hardest battle). It is fun to build new kind of strategies instead of building a diverse team. The last main game I have played was Platinum, so this game had many new features for me (Didn't even know of terrains and shell smash for example). When I was reading through the comments here, i saw a lot about ev training and having good iv's, that this is needed to beat the game. To those people, no it is not nescecary. I had for example a special Ninetales but when I was comparing stats, attack was way higher then the sp.attack. What i want to say, tactic is the most important thing to keep in mind.
I have one con, During my playthough i have found 1 bug which can make certain battles way to easy. The AI knows which item you are holding on your mon. So I had a Charizard X, and brendan in the safari zone, Koga and May were spamming earthquake and focus blast before i even mega evolved. So my response was dragon dancing, mega evolving and start sweeping with Dragon claw or shadow claw. maybe u want to look at this to fix to make it more difficult?
Great game