How powerful Revan was is an interesting question from a few different aspects.
We've been told he was very strong in the Force and clearly had great potential. That Malak deferred to him, and was afraid to face him IMO (regardless of what he says) is somewhat suggestive that translated into Revan being an excellent combatant with the Force and saber. After his mind wipe and reconversion, he tears through the Star Forge, so he was clearly extremely martially adept. Canderous refers to Revan touchingly as "The greatest warrior of our time," in his final influence dialogue if you bring him with on the Star Forge, and that says quite a bit IMO.
From his victories in the Mandalorian Wars, the Jedi Civil War, the respect he was given by the Mandalorians, and the rest we've heard about his prowess, Revan was by pretty much all accounts a brilliant military tactician.
Finally, combining what we know of Revan's action during and following the Mandalorian Wars from KotOR1 and 2, the scope of his scheming, while falling a ways short, is within the realm of Palpatine IMO. Hunting down a space station built by a lost civilization 20,000 years old, converting thousands and thousands to his cause through Malachor and more perverse methods, the assassins, the academy, etc...he was far more savy than your "Mwahahaha, I will knock you all down!" Sith villain.
Combining all of Revan's strengths, he makes one of the most formidable characters in the Star Wars universe. I don't know how I feel about him being as strong in the Force as say Exar Kun (who Jolee claims posed a bigger threat than even Revan IIRC), Vader, or Sidious, but as a total package he deserves to be in the discussion of those who wielded the power to make or unmake the Republic.