I enjoyed Nemesis a great deal. Shinzon was a believable damaged Picard clone, the Remans were cool (a big step up from the bowl cut brigade Romulans). Picard was feeling his age and the situation, the crew were feeling the gravitas of what was going on. What others here see as "out of character" I see as very appropriate. The action was fun. Even the dune buggy made sense IMO - were they expected to just walk miles between android parts? A vehicle for away missions is long overdue (although understandably absent in the TV series' due to budget constraints)
The bad was the wedding at the start, which was painful, much of the attempted humour sucked and Picard asking Troi to endure more of Shinzon's attacks was disgusting.
Picard running around the Scimitar with two phaser rifles, blasting away like an ancient John McClaine never fails to raise a smile. I'd pick that over watching him play the flute, play Dixon Hill, talk about archeology, have breakfast with Beverly, ponder the implications of the Prime Directive on a planet-of-the-week or walk around in his night robe any day.