This is going to be considered the one of the "first" VST commercial plugs that appeared on the market. This is partly true, but this doesn't mean the Atom Pro is "outdated". I think this is a simple, yet great instrument. Of course later plugs can do better, but I think it has a great value for money. I don't remember how much it costed (I think it was 20$).
It has some good presets, too. The sound is not so fat, but is capable of producing good leads and pads.

Pro:
+ simplicity makes it easy to use
+ great sound for it's simpliticity
+ MIDI controllable
+ support

Con:
- outdated GUI + features

Yeah, this was also my first VSTi I payed for in Spring 2000...

You can create a wide range of great sounds, and I still love it for it's simplicity. The perfect tool for enhancing your track for purposes when using one of those big complex monster synths is oversized...

Compared to nowadays up-to-date 'entry' synths it's a bit outdated in GUI and features, but a 'revised' version seems to be in the pipeline.

Atom Pro was the first VSTi I paid money for! And I still like its sound. But maybe it is a bit over age now...