It's difficult for me as well. I thought that making a devlog for games that I intended to finish would help me to finish them. Unfortunately, it just gets people saying, "Good job on that one - I can't wait to play it!", when I haven't worked on it in months. It's tough.
I also agree with you, orange08 - one of the only games that I pretty much finished and released was one for a weekend game creation competition. I took first place, I think. (No prize, though)
I think that I need to step back from the 'epic game' ideas, and either choose one of two paths.
1) Make short, simple, sweet, and fun games that are easy to make and finish, and build upon those.
2) Make larger games, but create them incrementally like MineCraft and Terraria. Those seem easier, since you don't have to worry so much about the harder things - just keep building on the actual game mechanics, and people will support you.
EDIT: And also, while I believe my favorite game genre is Metroidvania, a la Cave Story, I need to realize that that game took years to make. There's no reason why I'm faster than Pixel.