Not true anymore. The original park has the Mummy, which is an excellent indoor, heavily themed roller coaster. That being said, I'd still recommend IoA since it has more thrill rides and in my own opinion is the better park.
There is no shuttle service, and I've seen others mention a cab is about $40 each way. It would probaly be cheaper to rent a car for the day from one of the onsite Alamo locations.
If you can make it work out, It's definately worth the trip. IoA has been my favorite theme park since my first trip there back in 2000