The thing that stood out the most was how low-budget it felt. And not low-budget in a TFF way, because at least TFF had the scope and grandeur of a feature film. Everything in NEM was claustrophobic and cramped.
The sets all felt like TV sets. The Romulan senate, for example, was not the ominously enormous parliament one would expect of an alien planet but a couple dozen chairs on choir risers.
I too was also very disappointed in how small the Romulan senate was in Nemesis. It made the movie feel the opposite of epic.
It felt very straight to DVD or TV-movie in quality, for me. The only two parts I like in the movie is just before the main battle when the Enterprise crew is breaking out sidearms and getting the ship ready for the fight--felt like the "run out the guns" sequence from TWOK; The battle after the Romulans showed up, which was visually impressive even though the bits with the actors were pretty bad.
One thing that pissed me right off with the movie is the Troi Psychic rape scene. How many more times were they going to go that route with her? First the series, now the movie, couldn't they have cooked up some other threat for her?