I bought my son his first GeoTrax set when he was about 18months old, and I absolutely love it. Whoever designed the system for the curve radii, track pieces, switches etc., must have been a train lover because it is impossible to build a layout that will not connect to each other. Using the switches, I actually have constructed many point to point runs with auto reversing loops at both ends. Playing with Geotrax with my son has not only given us great bonding experiences, but I've used it to quickly test out different layout ideas and I've been inspired to new ones.
This is in stark contrast to both the brio and thomas the tank engine track systems. With both of these systems, it's can be difficult to bring tracks back into proper alignment especially for younger children.
I just figured I'd share the fun that we have with it, because I'm sure there's other dad's or grandfathers out there, just dying for a way to get the kids in their life into trains.