I loved lego as a kid, from when I first got some around the age of six until I went to college. I stopped buying new lego (it was very expensive then, and it's still expensive now) at around the age of ten. The "state of the art" of lego at that time was "electric lego" (when I visited Legoland in Lubeck in 1974 they were showing off the new 12v lego trains, but they weren't available for sale yet). Electric lego had been designed to operate train locomotives (the battery box became the caboose). It was clunky, and ate C cells for breakfast.
While I still enjoyed messing with lego, it faded as it became clear that lego was in a state of flux (technical lego appeared, the old "electric lego" faded away, and lego people went through a few design iterations), and besides, I acquired a computer habit.
I got a few small lego sets to play with. (I'm trying to come up with vehicle and spaceship design ideas for a game I'm working on, and it's so much nicer to mess with physical objects sometimes, and clay is messy and inconvenient ... although the new modeling sand from Play-Doh looks intriguing.) These kits are from the Mars Exploration set (white, grey, black, and orange, with green martians) which appears to be designed to smooth the transition from basic lego pieces (targeted at ages 5-7) and technical lego (which is really aimed at ages 10-13). This fills a discontinuity that basically blocked me from continuing with lego some thirty-four years ago. I guess progress in the toy industry is not quite so spectacular as in the computer.
One thing I always disliked in lego was single-purpose pieces. E.g. 4x1 pieces with car grilles printed on them. The most egregious example from my memory was a ship hull built of four pieces (prow, two mid-sections, and stern). These four pieces could be assembled to form any number of objects from a (1) ridiculously short 2-piece ship, to a (2) 3-piece "tugboat", and a (3) 4-piece "cargo" ship. Given that (1) was totally out of proportion this amounted to four pieces of lego that could be assembled into two different useful objects. This was perhaps the worst ever waste of plastic in the history of lego.
One welcome improvement in the new lego is the almost total lack of single use pieces (at least in the sets I bought). E.g. wheel axles in old lego came in two varieties. 4x2 blocks with sockets for wheels (which came in two sizes) to plug into and 2x2 blocks with either a pair of single or double wheels sticking out. Aside from creating vehicles which looked totally out of scale, these pieces were all remarkably ugly and lacking in versatility.
The new lego has "technical" pieces in the form of 4x1, 6x1, and 8x1 blocks with holes running through them (three holes in a 4x1, five in a 6x1, and so on). These look attractive (like struts) when empty and can accommodate a variety of small two-way connectors allowing sideways connection to standard bricks, small technical axles, and double-sided rotating sockets, as well as allowing technical axles to pass through. This allows technical components to coexist elegantly with standard components, and 90 degree connections to standard bricks.
The new lego also has a wide variety of hinges and joints attached to 1/3 height parts, allowing all kinds of interesting designs. Again, the single piece hinges in the lego of my memory were ugly and not versatile.
I imagine that much of this progress is owed to computer-aided design and improved plastics (the new lego feels less brittle than the lego I remember, while having similar rigidity).
It's nice coming back to lego and finding it familiar and yet full of clever, subtle improvements. By the time my kids are old enough to play with it, there should be a pretty nice bunch of it waiting for them. Used, of course.