It's not really a Greek restaurant, but I like Zalek's in Wakefield when I want a Gyro.
I've read good reviews here of Greek Grille in WInchester. I've only been once, and I thought it was fine, a little pricey. Not a place I'd go out of my way for, but my bank is right there so I'd go back. it's more of a takeout joint- they have a few tables but it's not a sit-down place.
21 Princess St, Wakefield, MA 01880
Grill the Greek
599 Main St, Winchester, MA 01890