Very few people are ever purely positive or negative. Rick Berman's strengths were as an executive producer on the logistical side -- he oversaw all the details of getting the productions made, from writing to casting to design to cinematography to editing to scoring to visual effects, and was remarkably effective at enabling TNG and its successors to achieve their high production values. He wasn't quite as strong on the creative side, but on TNG and DS9 he had exceptional showrunners like Michael Piller and Ira Steven Behr to handle that. The later shows had showrunners of more average talent like Jeri Taylor and Brannon Braga (and were subject to network pressures from UPN which hamstrung them creatively), and eventually on Enterprise Berman took on a co-showrunner role himself as Braga's full-time writing partner, something he'd never really done before and which wasn't his primary strength (his only actual script credits before ENT were TNG's "Brothers" and "A Matter of Time"). But his skills at managing the logistical side of the production remained top-notch, and every Trek show he oversaw was superbly well-made, whatever one might think of its writing.