Game making: playing a story...?

The reason I'm making a game is to tell a story.

Mechanics are nice, and graphics can be great, but the thing that really gets me and keeps me interested in a game are the characters and the story that they are a part of. For this reason I'm not a fan of MMORPGs, simulators, RTS, etc.

It's small wonder then that I'm focussing on writing out the story before doing too much in the engine itself. It's going to be a linear story (i.e. choices affect game play but not the ending). The challenge is to:

• leave flexibility open for the player to live out the story, not just have things cut-scened. This includes character customisation.
• keep game mechanics in mind when writing the story. E.g can a chase scene be a timed escape event? What event or character would be behind the puzzles that the main character would have to solve? Does crafting/classes make sense in this world?
• remember that this is a game and not a novel. Each scene needs something to keep the player interested in... well... playing.

So what keeps you interested in keeping on playing a linear game? Or, conversely... what makes you lose interest in a linear game?

I'm interested in your thoughts ^_^

Some of mine:

• clumsy mechanics (a certain level of mechanics-issues is overlookable, but just not too much)
• too many cutscenes that you can't skip
• too much text in one go
• characters that you don't connect with in the first 10 minutes.