After listening to Le Cose Che Non Dici fifty times the other day, I decided to listen to Rosso Relativo because I seriously couldn't get enough. I've listened to it four times now, to properly soak it in before making any type of judgment. First of all, the only other Tzn album I've heard is El amor es una cosa simple; I was really into it last Summer but never got around to listening to anything else from his discography, so I can't compare this album to any of his other work, really.
Anyway, the most obvious thing about the album is how infectious it is. After the second listen I found myself walking around my house singing all these Italian words that I had no idea what they meant- Di Pių, Perdono, Le Cose Che Non Dici and Primavera non č pių were probably the most catchy and easy to remember. Like you said in the OP, the album really carries the essence of catchy pop, which is good for two reasons: 1. I don't understand Italian, so having those catchy rhythms helps and 2. I just love catchy pop songs- but who doesn't?

Boom Boom and Soul-dier, for obvious reasons, stuck out a lot. I'm a sucker for a choir and BB was quite beautiful.
The more slow songs like Imbranato, Il confine and Mai Nata were good too. He has a really unique voice (or at least unique to someone not use to Italian vocalists) and a certain soul that stands out in a lot of the songs.
I'm going to listen to 111 sometime this weekend.

I know 111 is still pretty pop, but I'm a little worried about once I enter his more personal and deep work, when the lyrics will play a big part. I mean- I listen to a lot of J-Pop and don't speak Japanese, but still. I've read about some of the issues Tzn faced in his life, so it'll suck not being able to understand the lyrics.

I'm sure the emotion in voice will speak volumes though; music is the international language, after all.