A sure-fire way to maintain reader interest is to not tell them stuff, right? That way they'll keep reading just to find out, right? No. Utterly, utterly wrong. Giving the reader a question she wants to know the answer to is not the same as withholding the interesting stuff until the end. If you don't put the interesting stuff at the start then, well, the reader just isn't going to be interested enough to keep reading. It's obvious really.
The key is to give the reader interesting stuff right from the start with the promise of more interesting stuff and then keep delivering interesting stuff right to the end. Nobody said this was going to be easy.
The power of your voice, the detail of your description, the depth of your characters, all mean nothing if nothing ever happens. Your voice will quickly become droning, your descriptions pointless and your characters irrelevant and uninteresting if not tested by events. 'What happens next' is the simplest mechanism for narrative propulsion – don't be afraid to use it.
So your MC is a humourless plank? Or a spotless do-gooder? Or a bore? Or two-dimensional mouthpiece for your own Freudian hang-ups? I don't want to read about that sort of chump and neither do you. So don't write them.
Your scenes should be the natural consequence of previous scenes, and your ending should be inevitable but not predictable. If the reader has your plot figured by page 2 they are less inclined to read on to find out what they know already.
This doesn't mean you can't play with the form – many great stories start with the ending already known (which can have a propulsive effect of it's own), but unpredictability must remain - why and how did this known ending happen? How is this story going to get to that point. Inevitable but unpredictable.
Ok, so that's how not to do it - here's how to actually do it.