LT changed the league, because of the way Bill Belichick used him. He used Willie McGinest the same way, though McGinests skills aren't even close to LT's.
The way people are talking about him here, he was the waterboy running around, and that simply wasn't so. LT was great, but I don't see the chasm others do. Much of the dominance came because they also had Leonard Marshall, Jim Burt, Harry Carson and a number of other great D players to take care of in the front 7 of the Giants of the era.
LT didn't change the position, Bill Belichick did. He forced the 3 step drop, not the player. Again, he still uses it today.
I think Ray Lewis' dominance is moreso, because he controls the middle. Just like the Giant scheme was designed to put LT in position to make plays, so is the Ravens.
LT was great, and the first hybrid OLB/DE we saw, but let's not pretend that he was heads and shoulders above guys like Butkus, Lewis, Singletary, Reggie White, Deacon Jones. A place in history, to be sure, but if he was half as dominant as people are making him out to be, the Giants wouldn't have watched the 'Skins (83, 88, 92) make it to 3 SB's, with him playing (81-93), coming out of the same division. He was great, and dominant, but people are piling the accolades on a bit thick here.
A guiding force I always use when judging greatness is are they putting him in the position to be successful, and what is the supporting cast. LT had mounds of support here. It's why the Barry Sanders greatness is so impressive to me. He had horrible coaching and horrible talent around him, yet he still got it done.
As for the greatest FB player ever, I say John Elway.