What did you think of the waist level finder on the Rolleiflex? I think the big question is if you want a medium format Leica, continuing in the basic design and way of shooting. Or if you want something very different since it can open up new ways of shooting. For 'similar,' one of the fixed-lens Fujis would be your best bet. Or the Bronica RF645, which does have 2-3 lenses (one is hard to find, I think).
And for different, go for the Hasselblad. The ground glass viewing, SLR, and screen blackout- completely different way of shooting all around than the Leica! Bronica, Mamiya, Pentax 645 are other options in this world.
A Bronica ETR-type with a speed grip and prism finder handles very much like a 35mm SLR.