I was thinking about the game mechanics after playing various main pokemon games and saw things I liked, and others I did not. A few I remember are:
VS Seaker (Animation in FR/LG is pretty neat)
FR/LG/Platinum Move tutors... How I got a Poliwrath with metronome and Mega Punch
Battle Area in Platinum
Weather Effects and Day/Night system
Rebattling Gym leaders was a good idea
Rivals pokemon being strong if you beat E4 20 times in D/P
Contests - If they were made like Anime ones, they'd be much better
Poffins/Pokeblocks - No way to decrease a pokemons condition if it were not the way you wanted it
Event Pokemon - Not everyone can obtain them
Evolving pokemon through trade.. SUppose you want your powerful Kadabra to become an Alakazam and you can only do this by trade, and you want the Alakazam back, but you have no one to trade with, what do you do? Stick it on GTS and hope to find another great Alakazam on there?
Egg Moves being overwritten with new moves in daycare
Amnity Square - Maybe its better in the Platinum version, have to play and see
Ruby/Sapphire - Lack of some things to do, lack of wild pokemon with decent levels (e.g. lv35-40 or higher) It takes forever to get the pokemon to level 100 in those games
Lack mainly of something to do after beating E4
Anything you like/dislike about the game mechanics or whatever?