It doesnt run in the background, so it doesnt always remind you of tasks due until you go into the app to check. Its hard to see the point of a task app when it doesnt remind you to do the tasks. If all you want is a checklist, there are much cheaper apps for that.
It does have a bunch of other cool features, but I dont recommend buying it until they get that fixed.
aedifica about OmniFocus 2