I'm so impressed by this gym - it has everything a small baby needs to keep them happy and occupied. The mirror is the big winner with my 2 week old, although there are plenty of other great features to keep him happy as he grows. The plastic rattle will be great for teething, there are lots of crinkly toys for when he gets older and starts grabbing things, and the sounds and lights will be brilliant for tummy time (although I do have to say that I'm not a huge fan of the music - and it'd be great if the volume was adjustable).
I had a similar play gym from the same maker for my older children and it was wonderfully washable and robust, but I do have to say that this one also benefits from major improvements in storage - just two little metal studs to clip it together for storage / carrying - and then undo them again and it pops open in an instant. Brilliant!