As much as I enjoyed playing through the game and am sure I'll continue to enjoy it, it was an absolute cakewalk of a game. The EXP Share is certainly part of it, as it allows you to keep a fairly balanced team without having to split EXP between them to the extent you would have to otherwise (which would generally push the average level down), but getting experience for captures is another big one too, especially with the larger variety of Pokemon available in the game, and the amount of them stacked between the early Gyms, adding a whole ton of EXP gain to encounters that would typically be dry. I was a good 8 to 10 levels above pretty much everything the whole way through. Tore through the Elite 4 like they were the Hoenn League facing a Blaziken.
It's still a very good game, and there are ways you could impose more challenge on yourself if you really wanted to, but played as-is it's also a very easy one. Not that this matters too much of course, the real challenge in Pokemon has always been assembling your critters and battling other players.