The tangle is an interesting concept, but it has security flaws because of a low "hashing rate" at times with nearly no transactions that are happening. This way it can easily be attacked. It's also centralized now the way IOTA is doing it with a special node that delegates a lot of the transactions. Furthermore the internet of things is just not there yet and so the use-case is too early... And last but not least you could take that tangle idea and put it into a second layer scaling solution of Bitcoin or another protocol... you don't need IOTA for that (: