This is my first Android phone and after only a few uses I realised that the OS is a huge improvement over Symbian. The interface is very easy to use and only takes a short time to get used to, and the number of apps available is worth the switch alone.
Given the small size of the phone I was expecting the screen to be hard to read but the display is very clear. The touch function is well tuned and after a few prods getting used to where the touch reacts in relation to my finger (slightly lower than on my previous phone) I haven't had any problems clicking on what I want.
The phone is incredibly light - when it's in your pocket it doesn't feel like it's there at all. It also looks very compact; looked at from the front the dimensions are similar to a credit card, though it is considerably fatter depth wise. The fatness isn't really a problem though, as it feels right in your hand and your fingers naturally fit to the various controls and the screen. If it was slimmer, it might feel more flimsy. It makes larger phones like the iPhone look clumsily large in comparison.
This is the model with the keyboard. The keyboard itself is quite small but big enough to type on, and much more efficient than using the screen to type. If you've never used a phone with a 'proper' keyboard before it might take you a while to get used to the function key which is used to access symbols and numbers (some of the keys double up).
Overall, I'm very pleased with this phone and can't find many downsides to it. The only thing I think it misses is a d-pad or some cursor keys on the keyboard to let you navigate the display entirely from the keyboard. This is a fairly minor issue though, and is outweighed by the rest of phone. Love it!