I used to live in a Philly suburb, too, and have been in MA for a long time now. I used to think about moving back to PA, but I love it here now. I am more of a city person, and live in a city now.

Closest Rita's water ice: Looks like one may have opened in Walpole...they come and go in MA. I usually hit one in Vernon, CT (off 84) on my way back from PA. In a pinch, Richardson's (found in convenience stores, freshly scooped!) is not bad.

The thing I love most about the Boston suburbs is not HAVING to drive. I do drive around town for errands and to go see friends, etc. But for basic necessities, I don't HAVE to. This is great for getting purposeful walks in and being snowed in in the winter. Arlington has some cute squares and some buses to get you to a T stop and is pretty walkable. You'll love it! When I visit rural-ish PA, the driving IS easier with less traffic...but you HAVE to drive to even get milk.

Don't get your hopes up on pizza, but the area has a lot of good food you may not find in PA. This person made a google doc from a thread about restaurants that has good suggestions:

https://www.reddit.com/r/boston/comments/woc0dd/i_made_a_spreadsheet_based_on_ubitpushrs_post/

If you're a Philly sports fans, feel free to disclose it - no rivalries really with them.

As others have said, the great outdoors is not far away. Beach? Mountains? Hiking? Skiing? Biking? Boating? You can do it all with even a day trip. If you like kayaking, there are a few places along the Charles to rent (one in Kendall Sq too!). The annoying thing about MA is beach access, though I don't have too many comparisons. I used to vacation on the Cape just to easily get to a beach. The parking lots often fill up early or have restrictions. Revere Beach isn't too far from Arlington, and I go there a lot. It doesn't have a lot of amenities, but it's easy to park at, has T access (although from Arlington the T would be a haul), and is realllly big and doesn't often feel crowded.

Fall in PA is pretty good, but it's the best here. :)