Like I had a beetle mission with 35+ of the creepy crawlies where I expended literally over 600 rounds of ammo because rookies can't shoot for shit. it. took. for. ever.
Hell yeah, giant beetles and zombies will make any monster hunt last freaking forever. But I can remember the one of my first encounters with beetles somewhere in African Ruins. At this point I even had no vans yet - just a car. Yeah, right, two agents (one with Colt and another with Taser Pistol) against 12-15 beetles. I was really lucky by finding a good position atop of some ladder but even so I ran out of ammo very quick and was forced to melee. Standing knee-deep in the dead or bleeding beetles and hoping to survive another enemy turn... yeah. And then they (beetles, not agents) begun panicking
Chupacabras were very different colour. My first enconter with them was like "survive the enemy rush" mission from some RTS. Luckily, my agents killed most of chupacabras via reaction shots.
As for another monsters, none gave me so much problem as Swarmids. Thank god, I saw them two or three times only - and I barely killed one of them and retreated. Just becase you can't kill a freaking swarm with shotgun or SMG so easy.
But the worst news were Monster Attacks (ol' good terror missions with monsters actually). Giant beetles/spiders were okay (as long as you can consider monster rampage in the city "okay"), but shamblers gave me some hard time. And nothing was so bad as werebeasts. Fast, agressive and not so stupid like shamblers (who loved to "change their mind" in melee and go away) - nah, werewolfs/werecats are deadly in packs.
After all of this (and WTF-style zombie sightings in the Crop Circles missions) I hoped to never meet zombies in Monster Attack missions. And of course RNG was jerk enough to troll me with this when I met undead folks in some village. Thank god, there was no Infectors (I didn't even know about them at this point), or I would be really screwed.
Heh, and cultists are the story for another day