I like the Activity app, but coming from Garmin watch, I'm missing a few bits. Thought I share, as someone from Apple might see it and implement.
- Predicted finish time for distances. Very useful for racing. You could set up what distance you're running (5k, 10k, 21k, Marathon) and see predicted finishing time based on average pace.
- Current heart rate zone, when training/running.
- Best times. I'm surprised this is missing. It could show best efforts for running. 1k, 5k, 10k etc., so you can see how you're progressing. Achievements don't work for me at all.