Great thread idea. While I do have a bunch of unfinished games, I only return to a few special cases.
I've had Metroid Prime Trilogy on the backburner for a while now, to the point where I thought I'd never play it again, selling my copy for a cool £80 or so.
Then a day later the deal of the decade -- £8.99 digital Trilogy arrives. It'd be rude not to get it at that price.
Having read a few tweets from a first-timer praising Prime's atmosphere (from @retroed I think) I had to give it another go. And within a day or two I'd already passed where I was previously stuck on years ago in half the playing time!
I also have Kirby's Epic Yarn sitting atop my Wii U. I want to try the extra levels.