I've only had a couple of hours with which to have a play, but my impression so far is positive. Compared to the Acro S it's almost exactly the same size and weight, but it feels more solid - the squarer edges probably add to that impression. It's also incredibly responsive, much more so than the Acro S, which I suppose is to be expected given that the Acro S has only a dual core processor. I ran a quick benchmark in 3Dmark, and it scored 19227 on the Ice Storm Unlimited test, which is excellent. I'm also very impressed with the 4G and 5GHz 802.11n wireless. On 4G in my home in Croydon, I got 19.5 Mbps down and 17.82 Mbps up, and 60 Mbps down while connected wireless to my home internet connection.
My only disappointment is that the DK32 charging cradle isn't included, whereas the Acro S came with the relevant charging cradle. I suppose other manufacturers don't include charging cradles with their phones, but it's a bit of a downer. I'm not sure if I want to spend the £25 on the cradle when I can get a QI charging mat for half the price, but having gotten used to having one with the Acro S, I might just get one.
Edit: a quick comparison AnTuTu benchmark between the Z1 Compact on the left, and the Acro S on the right.