I just upgraded to the 235 from the 220, specifically because I was interested in the optical HR. First thing's first - check out the DCRainmaker review. Ray is pretty spot on - the HR is good, but isn't perfect. That's fine by me, as I sometimes have chest strap HR problems anyway. It's a trade of an imperfect technology for another one that's less annoying (I really wanted to ditch the chest strap). The optical is pretty useless during cold weather, which I knew going in, so I do still have to wear the strap for my long runs outdoors this time of year. However, Indoors it has tracked well, and I've liked being able to ditch the strap.
The surprise for me was how much I have enjoyed some of the other features. The 24/7 HR tracking automatically pulls out your resting HR each day and gives you a rolling 7-day average. I watched that figure go up and down as I got sick just after Christmas, and expect to see the same it I was starting to overtrain. I've also watched it nudge down as I've been working into my winter Marathon cycle. Really great data, which I'm too lazy to collect otherwise.
I'm also a chronic phone-ignorer (miss calls, don't return texts for days), and I think my family and friends have really appreciated that now my wrist jiggles whenever I get a call or a text. I know I have liked those connected types of functions. Connect IQ does nothing for me, but I certainly don't mind having the ability to fiddle with custom watch faces and apps that tell me the phases of the moon (or whatever).
The 220 was a little higher on the just-works meter, and was probably my favorite watch ever, but I'm happy with the 235 and feel comfortable recommending it. Just make sure you know what you're getting into with the optical HR (again, see DCRainmaker) - that will make a world of difference with your satisfaction.