Functional considerations: parking, displayed showtimes and pricing, payment options, price, bathrooms, seating comfort and arrangement, ambient sound and light, sound and picture quality, and membership availability. Aesthetic considerations: outdoor and indoor appearance, ticket format, free schedules and other flyers, cleanliness, and majesty (is it a movie house or a movie palace). Service considerations: box office attendants, over-all friendliness, presence of ushers. I will tend to exclude concessions from consideration, as I don't typically buy any food at the theater; so I won't be able to tell you who has the best popcorn in town. 1 star is a dump in a strip mall with broken seats, spotty sound, and a sticky floor; 5 stars is The Paramount Theater, where you walk inside and your jaw drops.
How entertaining is the trailer and how much does it make me want to see the advertised movie. I'll list the number of cuts from one camera perspective to another as a way of measuring the level of visual bombardment you can expect from watching this preview. A trailer can be good with only a few (like the charades trailer for Monsters, Inc.), or with a lot (the first trailer for Fantastic Four has 145 cuts). 1 star means the trailer is boring and I have little desire to see the movie; 5 stars means I immediately break into the projection booth and stage a sit-in until the theater shows the advertised film.
At its most basic, how enjoyable was the movie. Did it make me laugh, cry, think, grip my seat, stare in awe, etc. Was it well-made. Was my attention engaged. Were the characters believable, their dialog interesting, their expressions nuanced. Was the plot fresh and unpredictable. Were the costumes, props, and locations visually appealing. Am I a better person for having watched it. Was there a part for Julianne Nicholson. That sort of thing. 1 star means the movie was boring and a waste of time. 5 stars mean it was amazing, thoroughly entertaining, and (depending on the genre) I can't wait to see it again. On a rare occasion, and usually for a horror movie that I was tricked into seeing, I will give a movie no stars, meaning my life is actually worse off for having seen it (take this rating with a brain of salt if you like zombies).
One additional thing: I'll be date- and time-stamping my 100 movies with the date and showtime for when I saw the movie, so you might see the entry for some movies appear retroactively during the course of this project, if I delay a day or two in posting my response.