I have two things to say about TADS 3: a) as a programming language it's most excellent and b) the library is huge.
TADS's learning curve is very steep at the beginning but I have a feeling that once you get a decent grasp of the language you can do advanced stuff quite easily. With Inform 7 the learning curve is almost the opposite: you can get in with no effort at all, but when you get to the advanced stuff you hit a brick wall.
This is the third time I've started trying to learn TADS. The first two times the library was just too overwhelming and I didn't get very far before just becoming tired. Now I've picked it up again and it's going better than before. While I've never had as much fun programming as I have when working with Inform, TADS is also fun but in a different way: the feeling of harnessing its raw power is what makes TADS a pleasure to work with.
Just to tame this beast I'm going to do my next project in TADS. An old acquaintance is about to return...