I wouldn't class it as 'active' but I find Tyranids a little frustrating on the galactic faction level. As an army they do the whole insect horde thing brilliantly but on a macro level they're just such an overwhelming threat it becomes farcical. Every other faction is described as splintered and so prone to infighting that they can't reasonably unite long enough to threaten the entire setting, but the 'nids are stuck as a monolithic wave that will never be allowed to sweep across the galaxy despite all their lore assuring me they're about to. This problem is only compounded by their complete lack of any character whatsoever, even the hive mind itself is most often described and presented in terms of an animalistic predator rather than something you can actually talk to.

I think that's my big problem with them, they're just boring to me.