If I had been writing Nemesis I would have had Picard going up against a dark version of himself. Not an evil clone, but someone just as smart, capable, and experienced as he was. Think a Romulan Picard who is the shadowy reflection. Like Belloq to Indy in Raiders of the Lost Ark. He isn't evil per se, just he wants to get to the McGuffin first and while Picard has morals and Starfleet regulations to hamper him, Shadow Picard is willing to cut corners. He can have the Romulan military pushing him and even threatening Shadow Picard, but it's ultimately down to Picard having to outthink Shadow Picard. Of course there's a showdown at the end and the good guys win, but at a cost. Data's gone, the Enterprise is wrecked, the crew split up to new assignments, and Picard retired against his will, but he's good with it because he saved some planet or race or humanity or something and kept the McGuffin from the Romulans.