Although I never owned an ST myself, my brother in law still has one (a 1040Ste with 60 MB megadrive). As he stil doesn't understand computers at all, I had quite a good chance to take a look around.
I never liked the OS. Slow, no multitasking, small harddiskpartitions (about 16 MB max or so). I admit there are possibly newer & better versions of the OS for the ST right now, but that particular version of the Atari's OS did not even compare nicely to the Amiga's 1.x versions of WB/KS...
What I _did_ like was the nice black & white picture, the internal PSU and the ability to read/write pc-disks.
All in all, I prefer the A2000 for the better OS (even with 1.x), the great expandability without resorting to band-aids & paperclips to get it functional and the more practical housing it comes in...