One side benefit of downtime during the holiday season is the chance to return to my roots and play some computer games! Probably the most fun and addictive little game that I've played of late is Mini Metro.
Mini Metro has a clean minimalist look with a very simple interface and premise....don't let your passengers wait. If you keep the traffic flowing everything continues onward, once things back up for a certain amount of time the game ends. With multiple subway/metro/tube maps representing the geography of famous world cities to play it's an easy way to lose a few hours of time and has enough depth to it that it sits well above the majority of puzzle games I've played.
At the moment it's a computer game that is available via Steam, however I believe it's being ported to IOS and so should be available on IPads soon enough, where it looks to be ideal with a touch interface. It's a great deal of fun and comes highly recommended. Give it a look.