Flicky: The original Angry Bird!
I think Flicky could be a good competitor to Angry Birds if they gave it a reboot. I find the game very addictive and am pretty good at delivering all birds in the fastest amount of time (though I still have a while to go before mastering it). Anyway, this seems an unlikely candidate if you were to ask people about what SEGA franchises to bring back, but it's really not impossible and could actually work. It would definately make a good phone or tablet app, and a level editor would be nice.
So who else adores this game?