Not bad, but not great. SLJ's appearance wasn't a surprise - he'll appear in anything. The only thing that was surprising about it, was that it took two whole episodes before it happened.
Coulson isn't a cyborg/replicant or anything else. I'd bet dollars to doughnuts, they flew him back to Valhalla and dropped him in that re-gen chamber, that Odin was in, for most of the Thor movie. If it can bring you back to life, I'm sure it can plant memories, as well.
But for a super-secret top government agency, they sure are loosey-goosey on the security. "Oh, you're some chick that Phil boinked 10 years ago, and hasn't had contact with, since? Sure, c'mon aboard.". "Oh, you're her unverified security detail? You can come, too.". "Oh, you're a crazy hacker chick that we found in a van? Welcome aboard. And as a bonus, since we know you like to hack into our systems, you can absolutely keep all of your personal technology devices, and we won't even bother to go through them, to make sure they're secure.".
Apparently, it's far easier to get aboard a SHIELD plane, than a Pan Am flight. Want to get on a super-duper top secret government aircraft - right this way, please. Want to fly down to Florida to take your kids to Disney? Well, first we'll have to strip search your children, then send you through a backscatter machine, and please remove your shoes before going through the array of metal detectors. And unfortunately, you can't take your 97 year old mother with you, because her name appears on the no-flight list, as a potential terrorist.
-Fred