I watched Semantic Error for the first time several months ago, so I can't really tell you what are the differences between the series and the film - all I know is that they're very small differences, with no major changes. In case you haven't watched either and you're indecisive, I'd recommend picking the film if you have the time to watch the whole thing in one go (it's about 3 hours long). I feel like watching the film let me enjoy and understand all the scenes to the smallest details a lot better than the series.

I really wanted to write a review for Semantic Error, since in my opinion it's one of the best Korean dramas out there - yeah, dramas, not BLs. I rarely, if ever, use words like "masterpiece" to define anything, even when I really like it, but this time around I believe it's deserved, since Semantic Error has NO FLAWS.
- The story is a very well-made enemies-to-lovers romance. The two protagonists don't start off hating each other in a way that makes their romance seem impossible, but their mutual dislike also has solid foundations that makes it believable. The various events of the story all have the right time they need to be shown, and the pacing is immaculate too: at no point did I think that a certain part should have lasted longer, or that some events happened too fast or not fast enough.
- The characters are all great. The two main actors are very good and expressive, their chemistry is wonderful, and their character development is a delight to watch. The secondary and support characters are also well placed and well utilised, with a special mention for Jae Young's group of friends (looking so comfortable and at ease with each other like real friends is not easy) and Ryu Ji Hye (she had a hard character to portray and she did it so beautifully that she stood out to me a lot).
- The camera work and the small details here and there make the whole show much more charged of meaning and enjoyable. The symbolisms of Jae Young and Sang Woo's character development are powerful and enrich every scene even more, to the point that every moment of the story feels important and memorable. The music and the effects also played a huge role in this.
- As I watched the film and saw everything for the second time, instead of feeling bored or uninterested for watching the same things for the second time, I was surprised at how I took everything in and let it sink deeper. The more I watched, the more vivid the story felt. I loved it.

This is highly recommended for anyone who likes romance, be it BL or not, because it's just too good to miss. It's fun, it's enjoyable, it's romantic, it's sentimental, and it's just so well made. I feel like the entire production team put a lot of effort and care in this project and it shows. You can watch it as a series or as a film, just WATCH IT.