Look i love my DS, namely for Kirby, Meteos and Nanostray, but there's something in that last game that really pisses me off.
It's one thing to use buttons to control the action or to use the touch screen to control the action, but when you have to use both it's a bitch.
Nanostray is an amazing shooter, but the weapon switching controls are just nasty. You have to take your eyes off the action an look down to find the button, or rub around until you're weapon switches to the one you want. You can't feel for it so those are you're only options. It's really frustrating and it looks like this trend is due to continue.
I will not touch my screen with my bare fingers so that means i have to play with the thumbstrap and beleive me it's a bitch to use the normal buttons with that thing on. Another failing of the Touch/Buttons system.
Both of these are reasons why it hampers game play and hinders the experience but sadly it looks like many future games are going with the combo system. Viewtiful Joe DS and Castlevaina Dawn of Sorrow both plan on using the combo system and i'm sure many more will follow. Hell it's even starting to look like the Revolution will have this problem.
Maybe it's just me but i fucking hate it and i wish i never had to see it again.