To be honest, I'm really bad at assessing acting quality. I mean, I can tell the difference between Patrick Stewart and Tommy Wiseau, but I'm not comfortable making precise judgments on acting as I do for writing. I also tend to attach more importance to the latter when considering a movie as a whole.
Fair enough, but a good or entertaining acting performance goes a long way to save a bad line
Using Star Wars, while this is a trite and cliche line, the way Natalie Portman emotes it still makes it appropriately sad: I am talking about of course "Anakin, you're breaking my heart"
And a good or serviceable line can be hampered if the actor comes off as wooden or too far over-the-top, the former is what lines given to Mace Windu become. I mean just imagine how this line could've come off if Sam Jackson's signature style was used. "You are under arrest,...my lord". Goodness, it'd probably be something like "You are UNDER AR-REST Jedif*&(!", definitely more appropriate for the scene.