This is an awesome port. Koei crammed EVERYTHING into the PSP version, and I can now confirm that you now play on the full game maps instead of the smaller, broken-up areas of the previous portable Musou games. The opening cinemas remain intact too, as do character and weapon upgrading. The game's real time cut scenes have been replaced with stills, presented comic book style, but with full voice. This is pretty much the only change I'm seeing so far. Character switching is done by hitting left or right on the D-Pad. Other than that, it controls exactly the same, too. I'm tempted to throw this on my fat PSP and try out the 2P, too...
The rip I'm playing off of (game comes out tomorrow!) has zero load times. I'll try the real thing out tomorrow and see how it loads and fares when not at 333mhz. Right now it's running buttery smooth.