I think it does one thing VERY VERY well.
Carrying a bigger baby or toddler on your back. You can do front, hip and carry smaller babies, but there are other carriers that do that better.
This is my DH's and everyone else's favorite carrier - it's simple and appeals to the masses.
We are bring the ergo and several other carriers with us to WDW - I wouldn't even bring a stroller but my MIL wants us to bring one so that they can go and have a grandma day.