Re: timesinks. (Psychobabble engaged. You are warned.) Extrinsic motivators are what make games work; they are what distinguish games from play. They depend upon the player's ability to delay gratification to achieve the goals that they set around these extrinsic motivators. In an ideal game, everything that happens between reaching these goals is fun--never boring. That's the intrinsic motivation part, which actually makes it fun, and sets it apart from work. (It's also why some people actually enjoy their work to the extent that it becomes play, and some people dislike certain kinds of play to the extent that they become work.) It's a lofty goal for something to be intrinsically motivating for such a very long period of time, 100% of the time. Practically impossible due to the pratfalls of life, but not theoretically impossible.
A game obviously doesn't have to be fun 100% of the time to be good, so timesinks can be acceptable. But the calculus that needs to happen and never does is an assessment of roughly how much intrinsic motivation (play meat) is on the game's bones. The more there is, the more frequently and quickly players can be rewarded for their play (with progression... gear, levels, etc.). Older games like FFXI and WoW have tons of meat on the bone in terms of content (though the quality of the content counts, too), and could easily afford to be more giving of rewards, though they both have significant problems with their reward distribution and the way they incentivize the content. GW2 was an example of a newer game that gave these out too quickly and didn't incentivize the content enough (by using generic rewards instead of content-specific rewards).
So as a generality, timesinks are bad. Essential at times, but bad. However, that doesn't mean that a game never benefits from making things take longer. A timesink isn't just something that developers do to stretch out the content... things like gear upgrades and leveling are necessities of progression-oriented content (they're staples of the RPG), and faster is not always funner. Timesinks generally refer to the tipping point at which the designers have overshot the amount by which players have to delay gratification to reach their goals... when they have well past the point where playing the game was fun, and now are solely working at it.