Any rants or raves here? Worth a look at the exterior, interior or both? Is there a garden and fortess walls nearby? Hard to find?

It's the French Embassy.
You may give a look at
http://www.france-italia.it/ita/reseau/reseau_01.htm

It's a beautiful building exterior, but as far as I know the public is not allowed inside unless, perhaps, you're carrying a French passport...?? It faces a charming piazza, but otherwise there is little to draw you here. I wouldn't make a special trip, but if you're walking in the area you could make a detour.

ttt

The piazza is a nice place to relax and have something at the cafe on the corner while people watching. I know some folks who put it on their itinerary because it is the scene of Act 2 in Tosca, Baron Scarpia's "home base"...although, as another poster pointed out, the interior isn't open to the general public.
I do recall reading that there is a particular collection here that you can make an appointment with the French Embassy to see. But, I don't recall what the collection consisted of....perhaps someone else here knows.

I saw a little burb about a collection being there so I assumed you could go inside. Don't know how to do it. A couple of tour companies also show it as a stop on thier tours.

The Palazzo Farnese is, as others have said, a working embassy and closed to the public. The grand galleria has famous baroque frescoes by Annibale Carracci, but I don't think there's an art collection per se there.

Could you possibly have read about the Villa Farnesina at the north end of Trastevere? It has some wonderful frescoes, including one by Raphael and some neat trompe l'oeil ones. It also has collection of drawings and a small garden, and it's open to the public.

Then there are the Farnese gardens, on the Palatine hill, but I doubt that's what you're talking about.

KT, I think that's it! You can make an appointment to view those frescoes. I've never done it, obviously.