The formula for the perfect game may be an area of hot discussion, but most would argue that games that are easy to get into and difficult to put down goes along the right lines. Players' early experience of a game is critical: this is the period in which they're making up their minds whether to devote more time, and often money, to the rest of it. 

So how do we make games with a polished early experience? Let's take some lessons from a game which I think does it incredibly well, PopCap's Plants Vs Zombies.