Some interesting posts over the last day!
I think Nintendo, and the early wave of risk-taking and innovative third party support (Trauma Centre, Goemon DS, Pac-Pix), managed to carve out whole new gameplay ideas and mechanics using both touch and the dual screens. As Matt mentioned, having two screens helped expand the way touch could be used (a single screen would be covered by your hands, and may have been too diminuiative).
The two screens also expanded the number of ways the handheld could be held - think about book mode in Hotel Dusk, or the way Brain Training shows its information on the left hand side while using the right hand side for text input. It’s interesting reading this interview with Satoru Okada and seeing the reaction the team working on DS (then Nitro) had to Yamauchi’s suggestion that the system should have dual screens.
I got both DS and PSP at launch, and both systems felt like very different visions of the future. I think Apple eventually merged what both systems did well into one device - the iPhone, but looking back, PSP was overengineered. It was ahead of its time from a technical perspective, but a lot of that actually hampered the user experience and games.
For instance, Sony’s insistence on going with a widescreen display hurt a lot of the ports that the system got - it wasn’t uncommon to receive stretched visuals or zoomed in, blurry visuals. The UMD drive imposed long load times and short battery life. And the single, high resolution screen - beautiful at the time but plagued with horrible ghosting - was clearly difficult to produce with a decent refresh rate. The PSP did eventually receive a decent lineup of original games and proper remakes (Tactics Ogre!) once it became popular in Japan, but by then the DS had built up a mammoth library of unique games and experiences and iPhone/iPod Touch/iPad were bringing in the next wave of those.
Still, I love generation 7. We had two handhelds doing very different things leading to two entirely unique libraries of games. It was rare to see a game built for both DS and PSP because of that, but the size of the market meant publishers and developers could afford to support both systems with bespoke titles and even bespoke ports. Meanwhile, in the console space, while the 360’s success with online services influenced the PS3, the Wii ended up carving out its own unique library of games too as publishers tried to experiment with ideas that may attract new audiences (Capcom and Zack and Wiki, Marvelous and No More Heroes, Nintendo and Endless Ocean, Konami and Elebits/Dewy’s Adventure, Atlus and Trauma Team, Sega and Let’s Tap).