Problems in planets that Tublear mentioned:
Crysilis: No animations. This is an obvious one.
Industrius: I could be wrong, but I don't think any Industrius conversion has had proper masking, proper coloring, proper added tiles, all the tiles, and no inaccurate lazy "remakes" using mirroring.
Technoir: Yes, it's missing some of that stuff that makes a tileset a JJ2 tileset, instead of a randomgenericplatformer tileset.
Slugion: Poor masking, I think some missing tiles, and ugly added tiles.