I love Tetsu; I think he's one of the best.
Personally I think you're pretty safe with any of his CDs with Namlook, especially the Broadway series and my favorite: 62 Eulengasse (purchased right here at the Hypnos store back in 2000, I think!). Time2 is, in my opinion, the weak one there.
His solo albums are all really good until he got into his granular microsound phase (Tzadik/12K), which I personally find hard to listen to. I do like Yolo, though, very much.
I also really dig his work with Atom Heart as Datacide (though Ondas really tests my patience and I've got to be in the mood) and Masters of Psychedelic Ambiance. I like the two collaborations with Jonah Sharpe too, especially Electro Harmonix.
I guess the trouble was that all the really good stuff was totally out of print for a long time, like all of the best of the old Fax label. Some have come back on Ambient World, only to go out of print again, and it's still hard to get certain releases in any format. I guess Emusic solved that problem, but I recall a lot of the Fax Sub-label stuff was not carried by their service unless Namlook was involved with it. With the current economic clusterfuck, I bet you could find the original Inoue stuff on eBay cheaper than everóback in the early 00's it was almost impossible to buy anything of his for under $75 dollars.