I hope, that I'm not treading too much of the old ground here, but here are my assumed-to-be unpopular opinions:
– I don't like the negative spaces in feminine torsos. They don't blend against vast majority of backgrounds, and just feel odd when you stop to think about them.
– People emphasise minifigures way too much when grading sets. (Especially Star Wars fans.)
– 95% (if not more) of official sets are not display worthy due to understandable compromises, but can be good parts packs or modified to look good. Good MOCs/SECs also look great as display items.
– LEGO has never been neglecting Star Wars prequel trilogy fans. (Although I agree that they should make some more PT UCS sets.) It has however been slim pickings for ST fans for the last two years.
– People whine too much about things that they could easily modify in their sets. Almost as if they've forgotten what the main function of LEGO is.
– The superhero themes have went downhill ever since their emphasis moved from comic inspired sets to sets inspired by the film adaptations.
– The May The 4th promos that were small dioramas were much more interesting than the exclusive minifigures.
– LEGO leans too much towards America. (But this is just me being salty that Finland, a country right across the pond from Denmark doesn’t get a LEGO store with a pick a brick wall or all of the same promotions as people who are literally at the another side of the world get.)
– Bonus popular/unpopular opinion combo: LEGO should bring back LoTR, but it shouldn’t last any longer than it did the last time, since their shorter licensed themes tend to have higher quality builds and minifigs than the evergreen ones.