I think Mikhail Tal was the greatest player of all time ,before his health started to deteriorate ,his attacking style was so unpredictable and calculated ,I think he proved how good he was in his games against Fischer ,also his first World Title Match in 1960 against Botvinnik he played some phenomenal chess becoming 8th World Chess Champion .Sadly from there he started to lose his magic ,but I still love the way he got out of his deathbed and beat Kasparov in a Blitz Tournament in 92.
I think Tal probably had the greatest calculating ability in the history of chess. I've seen so many Tal games that just left me speechless. Things like trading a queen for a rook within the first 15 moves that, 30 moves later, eventually led to an unstoppable passed pawn that the opponent's lone queen could do nothing about...or giving up his queen because he saw some bizarre bishop, pawn and knight checkmate 10 moves down the line that nobody in the world would see...and things of that nature are just mind boggling (I wish I can find the games I'm talking about, everytime I search for Tal queen sacrifices, I get so many results that I can never find the specific game I'm looking for!)
His problem is probably consistency. He also had a lot of subpar play against guys like Petrosian, etc. It could be because of his health, it could be his high risk high reward style of play, or a myriad of factors. I think when he was at his best and playing his best chess, probably him and Fischer are the greatest chess minds (and subsequently, chess players, of all time.)
On his best day, I don't think anybody in the world of chess (except Fischer on his best day) could hang with him. I just wish he had more of those "best days." Of course, that's just my opinion, I understand the arguments against him.
Any discussion of objective strength of chess players should begin by realising that many of the best players today have spent eight hours each day since before they were ten years old studying chess. Lasker was a mathematician and philosopher who started playing chess at an age when Karjakin was already GM level. He didn't have the last 130 years of opening and endgame theory, all top games from those years in computer databases, engines to help analyse them, didn't have any coaches and didn't go to chess school. It isn't his "fault" that his great talent couldn't be enough to be as strong as the best players today, that have all these advantages, and that's also why all comparisons should be of comparative and not objective strength.