I agree completely. The thing can be had for $900 if you find a sale, it’s got 88 weighted keys that feel really nice (they impress my wife sufficiently that she’ll deign to use it, and she’s quite the piano snob), and some of the samples are simply fantastic considering the price. Anyone looking for a starter synth should take a serious gander at the QS8 lineage of Alesis synths, IMHO. I’ve monkeyed with softsynths, but I just don’t think in terms of computer keyboard strokes, mouse clicks, and little graphs of timing and pitch; though I suck at it, I’m a very tactile musician, and if I think in visual terms, I think on a staff. I was so disappointed that Garageband (Apple’s cheapo sequencer-, sampler-, softsynth- and recording-studio-in-one package) has no standard music notation option. Most of these softsynths are completely mysterious to me, as a result of their (to me) unintuitive interface and visual output. Give me black and white keys I can fumble over, pound on, lightly tap, or sweep my fingers across.
For the OP, I think good digital synths/keyboards ought to have keys with some sort of weighting to give them more of a piano feel, fine velocity sensitivity with wide dynamic range so you can really play expressively, “aftertouch” (which you can turn on and off), and some other effects like the ubiquetous pitch-bender and some jacks for pedals like sustain. I guess for real electronic brainiacs who can compose straight onto sequencers and do all the fancy looping, etc. purely mentally and visually, most of the equipment I’m describing is superfluous, but if you’re big on kinesthetics, a mid-range synth with decent feel and responsivity will make you so much happier than a piece of junk that makes some cool noises but is essentially built like a toy.