Usefullness isn't a major concern... because you can have a nice little app that is pretty crappy, and only does one thing, but it might make that one thing alot easier to do than normal and be used so often it might as well load on start-up... lol...
Features.. Yes, much like my list that i provided in the template in the other thread except centered more around apps than games.
Stability is always a major concern.
UI is
definatly important as CattleRustler pointed out.
Idiot-Proofing is always a good idea too.
Resources is a good one to add ( both CPU resources and install sizes etc for the app size )
Feasability, ie, how easy is it to impliment and use? Does it require alot to be pre-installed ( like DBPro games/apps need DX9 ) and is it so stupidly large with images/sounds that it takes half an hour just to download etc...
Hope I Helped...
Team EOD :: Programmer/Logical Engineer/All-Round Nice Guy