Just like anything else - X% legit and Y% scam.
No reason to get an ICO particularly when you can buy the coins on an exchange after it ends. I do some ICO's - there are a few excellent projects out there with very high potential. There are a number of crap projects to take the money and run.
Look for a product that is already making revenue or with a solid contract. Look for something that will use the coin to produce revenue.
Walton Coin looks good.
The openledger projects have a good shot.
Cardano seems to be strong -at .03 it's got serious upside potential. Still not on the bigger sites - when it goes there, it will jump.
It's high-risk, but the rewards can be 1000's of times the risk, so play, but limit capital input.