DeMignon: In my opinion, Bastion isn't a classic one-day-game. It took me 15h to complete the main story + some extras, but there were lots of achievements, extra levels and perfect level completions left. So to finish the game 100%, it'd take quite some additional hours. That aside, I think a game with a common playthrough of more than 12h doesn't easily fit in one day, but is rather a two day game.
Thanks, that definitely puts it outside of my parameters. I consider a One Day Game to be 5 hours or less. I'll put it from the list.
PaterAlf: I have two more games for the list:
Pitiri 1977 can be completed in 1-2 hours.
Sometimes: Success Requires Sacrifice can be completed in 20 minutes or in 1 hour when you want to try every mode.
Do you have links for these? I'm excluding certain genres, such as shmups and coffee break games, which by their nature tend to almost always fall into this category by default.
Meanwhile, just finished
FarSky last night with a total playtime around 4 hours, so onto the list it goes.
EDIT: I'm guessing that
</span> and the <span class="bold">[url=http://www.gog.com/game/pajama_sam_vol_1]Pajama Sam games probably also belong on here.