It all depends on the games ofcourse, which, in this case more than ever, determine a purchase of a gaming platform. Though the ELSPA dropped the daily (or was it weekly) sales chart of the system, support is still quite strong ranging from companies like Capcom, Sega and even EA.
Some smaller companies come with new kind of concepts specifically designed for the N-gage platform. I myself don't own one, probably never will, but a good friend of mine does. Heck, I think he has all the great games on the system. I played several games, including Asphalt, Colin McRae Rally 2005, Pocket Kingdom, Pathway to Glory and Requiem of Hell. Though I disliked the racing games, never been a big fan of that genre except for Burnout 3 and the upcoming GT4, all the other games were quite enjoyable.
When it comes down to the FPS genre, it has some fairly stable collection. Ashen looks nice (didn't play it) and Call of Duty seems to be a pretty good game too. But then again, see if you can test the system to the max. You can do a lot more than just play games, and I'm sure you can figure out what those other things are. Just don't see it as either a Phone-, or GamingDeck-only piece of hardware, use it both ways. And whatever you do, get the QD, hotswapping the games is a must.
Test it, with as many games as possible, before you decide to purchase one.