I bought the Samsung Galaxy Ace about 2 months ago, mainly because of the price. I previously had a HTC Desire on contract but my contract price had gone up so I didn't want to be signed up for another two years. Overall, I've been very impressed. For a phone that cost me £150, it has everything I could want and more.
The phone itself looks very nice. I have the white one just because I wanted something a bit different, and it looks quite high quality. I was worried it might get dirty easily but because the back is so shiny, any dirt just wipes off. It also feels well built - not too heavy but not so light that it feels cheap. The glass seems pretty tough. I've dropped mine a couple of times, once face down onto stones, and although the silver around the sides got a scratch, the glass isn't marked at all.
The touch screen is very responsive and the screen is very bright and clear. There is sometimes a very slight lag when using live wallpapers but its fine with normal wallpapers. My only criticism here is that it is quite pixelated compared to some newer/better quality devices. Having said that, even on web pages with lots of text, it can be read quite clearly without zooming.
Being on Android, there are plenty of apps available to download which is always good. Samsung also have their own app store pre-loaded onto the device, and apart from games, I haven't felt like much was missing. It already has on all the standard apps you could want, as well as extras that I've previously had to download such as Youtube, BBC News, navigation.
Overall, I have been very impressed. I was initially worried that I would be able to tell that it was cheaper than my old phone but actually it feels just as good quality and for a cheapish phone, it does the job very well.