looks good?
maybe simply measure them...

If you have 3 mm left, the it still looks OK, but begins to be very low for rain.
Keep in mind that even the new tire will eventually fail in rain. Just depends on speed and depth of water.

How long should they last?
No answer to that. Depends on style of driving and conditions.

Lots of city (stop/go) and 35k miles tires are gone.
Highway, moderate speeds, gentle on gas - 65 MPH and they can last 70k miles.
Highway, heavy acceleration, sudden stops, and high speeds - 80 MPH they will fail in 40k miles...

And if I wanted I could wear them down in less than 15k miles.

 

I pulled my factory tires at 35K. Still lots of tread but they were weak from the day I bought the car. Replaced them with Michelin Defenders and I can't believe the ride quality, wet traction, and braking.

 

Changed out my son's "Hankook" tires on his 08 Hyundai Accent 5dr at 28k miles..Had good tread on them but they were dangerous on a wet road... ( I drove it from Connecticut to Ohio and will agree they were horrible tires)

He also went with Michelin replacements and the first time he drove it that he could not believe the difference... He thought the car was naturally a poor handling car...and the difference was astounding...
Dave

 

He thought the car was naturally a poor handling car...and the difference was astounding...
Dave

I can't believe how many people blame the car for poor handling not the only contact with the ground - the tires.