Wrath of Heaven was pretty good, I hated the combat engine, but liked how the developers kept the stealth aspect true to the series, and the gameplay was much more streamlined. But the storyline was utter crap. "The magic eye compels you Rikimaru." When I first heard about that plot device I thought it was a joke, or a bad translation as I was reading the games script on GameFAQs. Oh yah, and Ayame seemed neutered and nowhere near as cool as she was in the first two games.
Fatal Shadows I felt was a step up, it was more challenging, the story was infinitely better, the new moves were cool and the stealth aspect was stressed out even more making the game even cooler. Oh yah, and Ayame had her edge back. Just the way she pissed off Rin just for fun made me applaud. But the combat engine was even worse, I groaned inwardly whenever a boss battle started.
As for the PSP tenchu, I can't comment since I haven't wasted my money on that crap system, and don't intend to until they get a few more must play games, and lower the price.
One thing I have always loved about tenchu is the music. It's always just so awesome and touching, even at it's worse (intro theme for WofH) it's still pretty damn good.