I got one to replace my iPhone 3gs, while my bf got the S2 to replace his 3gs. I actually prefer the HTC (I saw the S2 before I ordered mine, but I ordered the Amaze sight unseen). The S2 is so thin that it is awkward to hold, while the Amaze is much more natural, albeit bulkier. They are both infinitely faster and better than the 3gs, and although I was worried about them being too big, now the 3gs feels small. It is very fast between screens and on wi-fi. I have only tried the 4G twice, once at my house (downtown in a large city), and once in Disneyland, and both times it seems absurdly slow. I was getting 120 k down, 600 k up at my house yesterday, now I am getting 600k down, and 1M up at my house today. At Disneyland, I could barely even connect to Facebook, and location services would hardly load at all, I had to try a few times and it took several minutes just to get my location. I barely got 100k down on speedtest in Disneyland. The 4G icon always comes on, but I have yet to see any speeds better than Edge. I definitely want to take it out to more locations to see if the speed improves, but it seems like the two place I tried it should have good coverage, as they are in major urban areas. I have had no problem with the micro SD card. The battery life could be better, but I have been playing a lot with it, which would drain the battery on any device.
Overall I am very happy with the phone, and glad I got it over the S2. In addition to the physical feel, I prefer the UI of HTC, and from the troubles my bf is having setting up his S2, it seems like the HTC is easier to operate and customize. My only two complaints have to do with the 4g, which is something I need to look into more, and the lack of accessories. I could not find a screen cover or case anywhere in LA, over a week after the phone came out. Many of the suppliers are not even manufacturing items for this phone, and most websites only list universal products for the phone model. This is an issue that will diminish over time, but I am a bit spoiled from the iPhone, which has a whole aisle of accessories in the store for it before it is even released.