I watched each and every match of Rivaldo at Barcelona. He was a great great player capable of doing things very few players would achieve. And he didn't play all the time for an underachieving Barcelona. He was part of a fantastic team coached by Van Gaal that won 2 consecutive leagues and went to European Cup semifinals and cup finals. Watch this: Frank de Boer, Xavi, Figo, Kluivert, Rivaldo, Luis Enrique, Cocu... It was a hell of a team!
Later on he was left alone, it's true, and for some years he was the only reference of the team.
BUT, though he is one of the best players I've ever seen, it wouldn't make it into my "best ever" players, not even best brazilian players as others say.
First of all, Rivaldo was very good, but he needed the team to play for him. Any player with that trait is out of my "best ever" list of any kind. Rivaldo was a great scorer, but he always thought first about himself. He did a lot of goals every season but very few assists. But it's not only about assists, it's about vision, it's hard to explain. He was extremely talented at close spaces, dribbling, shooting... but he didn't have that "special" touch or vision that legends have.
As I say, I loved him when he played for us, but I hardly felt the same mesmerizing feeling that I had when I watched players like Romario, Cruyff or Laudrup.
Look at Ronaldinho, he performed at his top level for only 2-3 years, while Rivaldo was a key player for a lot of years. But the magic Ronaldinho had... that is unforgettable. Though Rivaldo probably scored one of the most spectacular goals ever. I watched it live!
BUT... he wasn't a genius. He did a lot of things right, but he didn't have that special something that makes a player unique, and as Ben and Gerd say, that uniqueness is what makes a legend.
On the other side, Ronaldinho was a bloody genius, as Romario was. I prefer Romario over Ronaldo for similar reasons: genius. Ronaldo was incredible, one of the best strikers ever and a genius himself. But Romario had that magical extra something, he won with his mind other than his legs. That's probably what makes Xavi a better player than the likes of Gerrard to me, for example. Xavi plays with his brain, and I have a special predilection for this kind of players.
My favorite 11 of players I've watched would be something like:
GK: Van der Saar, Buffon, Arconada, Casillas, Schmeichel, Preud'homme, Zoff, Shilton, Fillol, Dasayev, Kahn, Schumacher.
RB: Alves, Maicon, Cafu, Thuram, Zanetti
CB: Puyol, Maldini, Nesta, Baresi, Koeman, Blanc, Scirea, Sammer
LB: Roberto Carlos, Krol, Tarantini
DMF: Beckenbauer, Redondo, Vieira, Makelele, Rijkaard, Neeskens, Hierro, Desailly
CMF/LMF/RMF: Xavi, Iniesta, Matthaus, Platini, Pirlo
AMF: Messi, Maradona, Zidane, Zico, Hagi, Laudrup,
FORWARDS: Romario, Ronaldo, Van Basten, Cruyff, Hugo Sanchez, Eto'o, Henry
As I say, it's the list of the guys I've watch play football (mostly live, others through a lot of telly), so it's a list of the players of my life. Older players would make this list even bigger.