Kanto: Some are pretty good, but many are very boring. For example, Seel, Dugtrio, Magneton.
Johto: Very creative Pokémon with a few exceptions (like Yanma and Qwilfish, they're just not very interesting). Overall, my favorite gen.
Hoenn: Even more creative than Johto, for reasons listed in an earlier post. But for some reason, I don't like them as much as Johto. And a few are flat-out bizzare, like Tropius, Nosepass, and Luvdisc.
Shinou: Meh, I dunno. Lots of the Pokemon here are evolutions and prevos. And while I don't mind that, the majority of them are too similar to their previous forms. For example, look at Etebossu (Aipom) and Mojanbo (Tangela). Things like the Minomucchi line almost make up for this, but many of the others aren't too great anyway. And am I the only one that noticed how like 70% of the new pokemon are blue or purple? I don't know if that bothers anyone else, but I like a variety of color. And aside from a couple Grass types, there's almost no green.