I learned from 4e:
I never want to have to go back and look at a book to make a ruleing during play: Clean clear logical rules/numbers that I can easily remember off the top of my head or guess at but remain fair. Great stuff. Having to figure out the DC for scaling a wet rock face with a strong northerly blowing ... no thanks. Easy, Medium, Hard ... that's all I need to go on.
I don't like Wizards with crossbows: At will spells are great, and make sense. A wizard with a crossbow does not. Characters should be able to do what they do. I love the idea of at will powers. I don't wnat to see this feature go.
I don't like Wizards with 1 hp: I remember 'selling' the awesomeness of playing a wizard to a new player. "Once you hit lvl5 you'll be awesome ... until then ... blush*" I remember zero to hero with a certain degree of nostalgia. Build the option. Don't force it on all of us please. I like my heroes heroic. I don't like someone sitting in the back accumulatin xp til the are reborn as a god.
I like fighters/bards/monks that aren't a crap option: I like balanced classes. Sure make them different, flavorsome. That's fine. But they should remain equally as good as the other. Every option should be a good option.
I hate the rat but I love a swarm of them: Swarms are cool. I remember playing an adventure with a group of players new to rpg. I acutely remember the disgust of the barbarian who failed a number of rolls against a diseased rat and his absolute exasperation as he failed to accept that his mighty warrior couldn't just stamp on the rat with his foot and be done with it. Now a swarmof a hundred or so rats. Much easier to imagine the difficulty to deal with such a threat.
I love my PCs opening a door to find 30 bad guys in the room, and they all draw their weapons ...!!!: Yep, I loves me some minions.
I love tactical combat where terrain is exciting, dynamic and meaningful: Sure, make combat fast and slick. But don't lose what has been won. Meaningful interaction with terrain is awesome. 20 ft by 20 ft stone rooms and fights in 5ft wide passages are not.
Saying YES is awesome!!!: My players can have an input!!! What!!?? That was my first reaction. I have since learned, saying yes (usually yes, but... but sometimes just yes) makes the game experience so much better for everyone at the table. Thank you 4e for teaching me that. It's the most important thing I have learnt during my years of DMing
I can name heaps more stuff, positive stuff, but I must be away. So, a few negatives.
I want interesting equipment and magical items. I'm not so much interested in the + on the sword, i want it to be awesome, memorable, special. I don't want it to break the game. If this means less stuff, no problem.
I want interesting features related to my charcter to do outside of combat: Self explanatory, but I don't want combat to be the be all and end all of the game.
More later!