The animated series is seriously underrated. I long for the day when Cartoon Network is wiling to risk something like that in their "Adult Swim" block. It should have gotten far more respect than it did.
As for Niven, Well, with Poutnelle he rocked. Lucifer's Hammer is still my all time favorite SF novel. But alone? Well, after years of hearing how it was a classic, I came across a used copy of Ringworld and was...underwhelmed. It was a nice enough read, but I didn't pick up on the characters nearly as well as I do with Heinlien. Card, though, I have enjoyed- what little I've read of his work (so much to read, so little time!!)
Adult Swim is too busy ruining great shows by horribly dubbing them (but at least they don't try to remove all blood, booze and cigarettes, which gives some silly results).
Niven and Pournelle, together, are far better than either alone. But I can read Pournelle's single stuff, and Falkenberg's Legions was great. Ringworld... well, it was a really cool concept but the execution was flawed. Niven's best single stuff was "Crashlander" and "Flatlander", IMO. Especially "Flatlander".
Ringworld's not the best book to start with with Niven, I agree. It was pretty slow in parts (though I did very much enjoy the Kzin and Puppeteer characters). Niven is very much "hard" sci-fi, and that book in particular was more interested with setting out -how- the Ringworld could actually function then in telling a story. It's sequels are actually a bit better, IMO, cause he gets past that somewhat.
Another thing about Ringworld is that it's pretty much the culmination of the entire Known Space series, which I think is in total now almost 20 novels and short story collections. Ringworld comes at the end of his "future history", and there's a lot of good little nuances that you miss out if you haven't read the backdrop.
The way I would start with Niven's solo works would basically be to start going chronologically into the Known Space Universe. Try starting with World of Ptaavs, Protector, A Gift From Earth, and almost any of the short stories surrounding Gil "The Arm" Hamilton. That way, you get a better idea of how we got -there- (Ringworld) from -here- (Protector, in particular, is key for understanding what went on in Ringworld). The short story collection "Tales of Known Space" intersperses stories from throughout the entire 1000+ year future history, and thus gives a very very good general overview.
Qwinn