Freshest in my mind is a game against Discordian using the new GK codex. Way back when, my Plague Marine squads with meltas and flamers could withstand the heat of close combat and act as a tarpit unit. If they touch virtually any unit in the GK codex in CC, they will be wiped from the board either that assault phase or the next. It's also a losing battle against Dark Eldar and their Wytches. My durability is matched by dodge and FNP, my hidden power fists are ineffective against dodge, and my toughness is negated by poisoned Agonizers.
Daemon Princes and CSM Terminators will have a hard time against Grey Knights since they lack frag grenades or the initiative to beat halberds. A Librarian attached to a squad can cast a reactionary sanctuary making the assault into difficult and dangerous terrain. Without psychic defense or frag grenades, those two potential CC beasts get slaughtered. It's almost safe to say that GK Librarians will be ubiquitous in non-Inquisition lists since they're so amazing. A Grand Master and Librarian provide so much flexibility to the whole army, it's difficult to counter.
What's the answer to this bizarre CC prowess in the newer codices? Shooting. Had I taken more than one Obliterator squad and turned tail with my Plague Marines and Princes, I might have stood a chance against Discordian's Grey Knights. The Psycannon shooting isn't incredibly threatening, and dual AC Dreadnoughts die easily enough with AV12. I am even getting driven more towards the idea of only plasma Plague Marines, and perhaps in minimal numbers. They're just tending to be ineffective in a lot of situations where I need them to have staying power. On a side note, if you can disembark enough of a Dark Eldar army before they are in striking distance, you win.
I find myself getting backed into a corner and having to play very defensively against newer armies. What situation do you find yourselves in when playing these difficult enemies?