Summary: upgraded from 610. best pros: lighter, skinnier, first gps i've had that feels like a regular watch. wristband is also more flexiible. much faster sat acquisition, within 5-10 seconds. more intuitive programming, i.e., intervals are just one tap away from run page now.
Summary: My old metal backed 610 died and I needed to replace it, so I got this. I can't be happier, lighter, more features, easier to use. I really like the fact it does cadence without any add-ons, I didn't realize it did it. I picked this over the 220 for the wifi sync, which works flawlessly.
Summary: My wife is a serious runner and had an older version of this watch so I bought this for her as a present to upgrade her old watch. She swears by this watch and won't think of leaving the house to run without it. I like the fact that it has GPS tracking on it.