People were hyping 4th Hokage as an awesome, strong character. People called the 2nd Hokage a scrub, he was weak. How the tides have turned. Minato is a bigger one trick pony than Kakashi. 2nd Hokage was beastin on Obito (Six Sage mode) helped take him down. Minato is the Vegeta of DBZ. Everything is his fault. He is the reason for everything. When I mean people not specific to GAF of course.
Minato would handily beat Tobirama. He's already got him beat in the one attribute they share most: speed. On top of that he's got Uzumaki clan sealing jutsu, barrier jutsu and superhuman reflexes the likes of which A's are
compared to. Minato is the only known character to have a flee on sight order on him during any of the Great Shinobi Wars. How freaking cool is that?
Also, consider the fact that, while yes, Obito was around 15 years old when he beat him, Minato figured out the mechanics behind Kamui within mere moments. It took the combined efforts of Naruto, B, Gai, Kurama, Gyūki and Kakashi to fight Obito for quite some time before Kakashi figured it out after noticing a crack.
Minato's analytical skill nothing to sneeze at.
Note, this is all considering him without his own jinchūriki abilities (though he lost those).
Lastly, while Minato died young and before making any significant changes, Tobirama set the gears in motion for the entire world to plunged into danger. It's characters like Tobirama (and Danzō

that place ruthless, dogmatic pragmatism above all else that perpetuate the broken machine that is the shinobi system, i.e. the cycle of hatred, whose casualties ultimately culminates in characters like Orochimaru, Nagato, Kisame and pretty much every other noteworthy villainous character.
@Winterfang - you don't seriously think Kabutomaru could beat Itachi, do you? Itachi saw himself in Kabuto and did him a favour by using Izanami. Had he been serious, that fight would have ended differently.