I have had both the ZD101's and now the ZD201 and I can say without a doubt that the ZD201's are hands down better than the ZD101's in every possible way imagineable. Visual quality is about the same (both are amazing), but that's where the similarities end. The construction and design of the ZD201's are masterful. They are THE best DLP-Link glasses available, and I have no idea why Optoma has chosen to not sell them in the US. People really need to write them and let them know that we want these in the states (I already did).
The ZD201's are the most comfortable and lightweight active glasses I've tried, yet they fit a big head like mine with ease. They fold (ZD101 did not) down to the size of a normal pair of reading glasses- it's hard to believe they even have any electronics inside. The arms on the ZD201's are rubberized and extremely comfortable, do not clamp down on the sides of your head and cause discomfort like the ZD101's. That's the main reason I got rid of them. Storing the ZD101's were a pain also, due to them not folding.
It's the little things you notice too. The hinges on the ZD101 did not flex and the arms were constructed of very flimsy plastic that were susceptible to breakage. The ZD201's have hinges that flex both ways and make them perfect for any sized head. The battery compartment is greatly improved- they now use only one battery and you no longer need a screw driver to change the battery. They have a very nice little slide out cover and you just pop it in. Also the lenses have much less glare than previously, thanx to a very nice little visor that is on the top inside of the glasses, blocking light from sneaking in. You do not notice it at all when you're wearing it, but it really helps. Finally, they just look 500 times better than the ZD101's. The Zd101's looked comically big and nerdy (not in a good way), and were just heavy and akward. It boggles my mind that they decided to keep selling them in the US and not the vastly superior ZD201's, but anyways, they're available on Ebay and Expansys-USA, so it's really not that big of a deal.
TIP: If you don't wanna put up $100+ for a pair of 3D Dlp-Link Glasses, then I would also highly recommend the new Rechargeable True-Depth DLP-Link Glasses sold on Amazon. They are the only other dlp-link glasses I've found that can compete and they are very affordable. They're about $140 for 2 pairs. They have everything that I like about the ZD201's, and even come with a pouch and cleaning cloth and a reverse sync button, which I know is important for some people. I currently own a pair of the ZD201's and 2 of the True-Depth's and I am very happy with both. Trust me, I've tried every dlp-link glasses out there, and for anyone with a pre 2010 DLP television, these are the only 2 glasses worth your money.