A few thoughts: Not many people know this movie, but George Lucas fans should give it a look, as it reveals the eerie potential he had as a filmmaker of more high brow science fiction. Is it anywhere close to as good as Star Wars? No, but it occupies a completely different space. A stark dystopian set entirely within the massive construct that seems to house all of humanity, THX 1138 paints a pretty bleak picture of a society where emotions are outlawed, and people are forced into sedation as a means of being more compliant. This is a visually fantastic movie, utilizing stark whites and sterile environments where other movies might take on a more dark look. But somehow this stripped down approach is more fitting. It's a solid script, but it definitely relies more on visuals and atmosphere than it does on story or characters. Sadly, Lucas did what he does and felt the need to pump it full of distracting CG for its re-release, but what else could you expect from him? It's still a solid movie either way.
Who would I recommend it to? Anyone who wants to explore the Lucas filmography or anyone who's serious about digging into '70s sci/fi should consider this a must-see.