I'm pretty new to this all, but have immersed myself pretty fully into the whole paper terrain world, so I'll give you my thoughts on them:
TLX is a system where you build invidiual components (floor tiles, walls, posts, etc). Once you have these pieces built, you can then quickly and easily reconfigure them with countless variations to produce a playing area rather quickly. And then when you are done, you can break it all down and store it in a few containers, as each piece is nearly flat.
The older, non-TLX sets are more "static builds" -- rather than building up reusable components, you build specific set pieces that are purpose-built for a single use. Typically you would glue the floor pieces (whether they be streets, grass, water, etc) to a larger "masterboard" which is a fairly big piece, and then attach your other components in a fairly permanent way. Once you have something built, it is typically "built" and can't be re-arranged on the fly.
Personally now that I own some of both, I don't even want to build the non-tlx stuff for the most part! It takes up a lot more storage space and lacks versatility. I've only build about half a dozen TLX tiles so far, and I am fully in love
