During the first season of Enterprise, I found myself liking Malcolm. His semi-reclusive nature was endearing, as well as adding a certain level of intrigue to the character. However, the show seemed to stick with that character outline without ever fleshing it out.
Over time, it felt like Malcolm was getting over-looked, which made him appear to be more background than anything.
It might have been interesting if Malcolm met an untimely death while in the line of duty, which would have been on par with his character, and possibly bring in a new tactical officer, such as Major Hayes.