actually, the only think great about IOTA is zero fee and it was an old coin.
If it survive through the past years, it will develop stronger.
The % of people trust new coin is decreasing, they prefer old coin with developing.
If you don't know then IOTA becomes more stronger and faster as more people start using it. And as its user base is increasing its transaction speed has decreased tremendously. So like you said theres not just one good thing about IOTA but numerous that will make this whole page short if I start typing.
As per My understanding
IOTA has 4 HUGE advantages over Blockchain cryptocurrencies in that it is:
Scalable
Decenteralized
Modular
Fee Less
Unlike Bitcoin which uses a blockchain architecture for maintaining its ledger, IOTA uses the Tangle which is a Directed Acyclic Graph, known as a DAG.
Tangle solves both the scalability and transaction fee issues, This removes dedicated miners and makes the system fully decenteralised.