X-Com 3 brainsuckers were but a poor imitation of the true terror that were Chryssalids. Real-time combat didn't help them either of course, but even with that taken into account a Chryssalid was a far scarier foe.
They were, essentially, like adult Xenomorphs, only harder to kill and incorporating a turbocharged facehugger capability. These things would shrug off bullet and laser hits and even take plasma in the stride, with only explosives having any real degree of effectiveness against them. I've seen a single Chryssalid destroy a 12-man squad almost on its own during a night terror mission. And by the time it was done there were seven Chryssalids...