It's quite interesting. I skipped generations 4 and 5, not because of the Pokemon therein but because of the series itself. I just got tired of the same ol' same ol'. I'm almost glad generation 6 is based on France, because one thing I'm certainly in love with is the aesthetics of this game.
By and large, there's a number of Pokemon from those generations (namely 5) that are really cool or cute, and I had to have them with me. Granted, there's still a lot of "I didn't miss anything" or "dang I dodged a bullet" mons, as well. Of course, every generation has these. Sigilyph and Emolga are new favorites of mine, and Ducklett is rather appealing, despite that I never played with it yet. I also like the chinchilla Pokemon, but like Ducklett, have yet to mess with them.
Newest love is Aromatisse without a doubt, though I'm a bit underwhelmed by how under appreciated it seems to be. That translates to I expected more fan art. D: Flabebe's line deserves a shout out. Fennekin, who I snubbed at first on grounds of being a Vulpix knockoff turned out to be really cute, and now there's room for both of them. It helps that Fennekin evolves into something totally different, much to the chagrin (and my pleasure) of those who really did expect a Vulpix 2.0. Or, you know, you could just go get a Vulpix?
I'm still not with everyone else on the Goomy train, but I'll admit the line is charming and Goodra is just as cute, if not moreso, than Dragonite. It'll take some time before I'm completely won over.
Overall, though, I like a lot of the Generation 6 Pokemon, about the same as I do Generation 3, which makes me feel that "less is more" isn't just an old saying.
Finally, as for older Pokemon, I've always liked everyone (just about) in Generation 3, so it'd be a given that I'd enjoy them here. While I still prefer Kirlia, Pokemon Y has given me some new appreciation for Gardevoir for some reason. I'm not sure why. Probably the scenarios that play out in my head more than anything else. Same thing goes for Roselia, who I've always liked for its design, but never really played with until now. Mawile has always been great, no surprises there. I also still prefer Flaaffy by a long shot, but I do like Ampharos's Mega Evo.
Nothing can or will replace Nidoran/ina, though. Amie doesn't set a case against them, either. I literally laugh when playing with Nidorina, and Nidoran Female is just adorable.