LogFAQs > #963504288

Synchro, Xyz, Fusion, Link. Pendulum.

Pendulum has way too much going on for one mechanic, I'm amazed they printed it for children and expected it to work.

EDIT: In slightly greater detail...
Synchros are nostalgia. 5D's was my favorite and made synchros look awesome. Many of my favorite cards are synchros.
Xyz are pretty cool, but they've become inundated with free rank-up cards, which I hate. Zeus and its ilk. That stuff shouldn't have been printed, make people use a Rank-Up spell.
I like fusions fine, but they push a little in the cheaty direction as well. Fusion summoning out of the graveyard is one thing, but if you're doing it out of the deck, or from your opponent's field, or not using a Fusion Spell at all, that's out of bounds in my book. Gets away from the original premise. Also when the materials are excessively generic.
I don't have much experience with Links, and haven't played a Link-focused deck. I don't like the linking mechanic too much, though. Mostly neutral.
Pendulums I explained above.