I'm pretty happy with what I've seen, although the CR 1/2 thug NPC is a nasty bit of work. Decent HP (30+) and multiattack. A 1st level party running into a pair of those guys might be in real trouble. I think the thug is the only creature that's really got a bit of side-eye from me around the CR. I think it's more dangerous than the hobgoblin, and I sort of pegged the hobgoblin near the top of dangerous CR 1/2 creatures.
I know my players would probably nominate some other creatures. They lost initiative to a chasme demon a couple weeks ago. CR 6 creature versus 4x 5th level characters. The chasme scored a crit on its first attack. For the record, that's 22d6 damage. It clean back-doored the target PC, not even counting it's "instant death if necrotic damage reduces to zero" ability. But then, the chasme's comparatively low AC and HP meant the surviving three characters killed it in two rounds, easily. As one of the players commented to me: "It's rocket tag. You get hit, you die. But same goes for the demon." Similar situation with the NPC assassin, or the intellect devourer, or the flameskull. If the party loses initiative (or, worse yet, gets surprised), they might be dead. But if they win initiative, the creature might be dead without even taking an action. So, the CR is probably appropriate.
The DM just needs to be aware that certain creatures are built to be extremely swingy. I wouldn't change that, by the way. I think it's great that there are "glass cannon" options in the game (as opposed to 4e, where there were virtually no glass cannons, and the players could be almost assured that no fight was going to be over in only 1-2 rounds). It gives the DM more tools to run the sort of game they prefer.