The biggest problem with old games on mobiles is definitely the controls. If you have seen Duke Nukem 3D on iPhone you would have to agree the controls make it nearly unplayable. I remember playing through couple of levels on my N810 and the keyboard makes it more playable but it can still be tiresome experience for your fingers. Connecting Wiimote to N900 gives good controls but the Wiimote is too big to carry around.
On positive side, porting games like these to n900 is pretty easy. So far I've seen Star Control 2, Quake 3, Jagged Alliance 2, Duke 3D and Shadow Warrior. All were ported by someone for free. If you connect Wiimote to N900 and N900 to your TV, it's almost as good as cheap console.
BTW, Quake 3 would probably have made a more impressive headline =)