Diana Muldaur is a very classy person (I had the pleasure of meeting her at the Las Vegas convention this year) and has never come out and said it directly but she's strongly hinted that she had a terrible time on TNG.
There was tension between Muldaur and the majority of the cast from the start. First of all she was coming in to replace Gates McFadden who had been fired because of disagreements between her and Maurice Hurley over how her character was developing (or lack thereof). Patrick Stewart in particular was appalled by McFadden's firing, which he made no secret of and openly campaigned for her return.
Second, Muldaur joined the show as a personal favor to Gene Roddenberry whom she liked and wanted to work with again. Because of this Diana got some perks the other actors didn't namely she was paid more than everyone except Patrick Stewart (we forget it now that while not a household name, Muldaur was a very well respected character in Hollywood and could demand high pay). Also Diana hated the one piece spandex Starfleet uniforms so Roddenberry ordered a special two piece uniform be created just for her (the rest of the cast had been campaigning for more comfortable uniforms since the start). Finally, because of her status in Hollywood she was to have been listed before Levar Burton in the opening credits but the cast protested so Roddenberry and Muldaur decided she would be listed as 'Special Appearance.' These things caused a great deal of jealousy and bitterness.
Muldaur admitted she found the whole experience very uncreative and she hated all the tech talk. She only signed a one year contract so when the year was over she had no intention of returning.