GAMEPLAY
The player must be constantly engaged, and suprised. The skills required of the player must change constantly to keep the gameplay evolving and challenging.
If your doing an arcade game, it may be important at the start to shoot all the baddies, but then get the player to dodge stuff - then get the play to run in amongst the baddies and collect a power up - then get the player to use the scenery and so on.
In a puzzle game, you can't just throw the same puzzle at the player continuously but with more coloured balls. You need to change the layout entirely between levels.
In an adventure game, and so many DB RPG projects fail here, you can't just throw a load of background story at the player and expect them to be a) interested in the slightest and b) thoroughly engrossed in plot and intrigue.
If there is a really vital plot point - do it as an FMV to get the users attention, otherwise shut up!

To keep an RPG interesting you need to throw different monsters at the player, that need killing in different ways. Don't just add 10 hit points to the boss mob, change his AI or lay the dungeon out in such a way that the player has to think about how to kill him.
Although i've postponed the project in my NFP game I designed an encounter where the player had appalling melee skills and a few minor attack spells - yet she had to take on a mighty Troll, the way to kill him is to use the most innane of her spells to entice him over a cliff.
In a race game, circuit design is 50% of the game, a bend with the turning after a crest or a 'thinking mans' corner like Russel Bend at Snetterton. The other half of the game is the AI - I don't know about you but i'm sick and tired of commercial race games being in the vein of 'overtake a load of cars, watch an accident with loads of debri and spin out when the phone rings so overtake a load of cars again'. I want to come out of the pits on a full fuel load and get the lighter, faster Ferrari overtake my clapped out Jordan. I want to battle for position with another car for 10 laps or more because he is slightly faster and all over my rear wing.
The only exception to 'gameplay is god' is if your doing a beat em up, then really all you need is lots of amusing weapons and a good particle effect for blood.
Pneumatic Dryll
