Playing style - what is appropriate?

I think in large part it depends on the breed.  My cockers never played as rough as the gsds do.....gsds can look and SOUND like they're killing each other when in reality they are just playing and having a great time.
 
Anne likely could give you better advice on specific breeds.

every dog is different.
 
sparky has a best friend since he was a little pup...one of their favorite games is where he lays down...she grabs him tightly by the neck...and he has to figure a way to wiggle or bite his way out of it.

Wesley likes to play rough and I let it go when the other dog is playing in the same manner.  I never let play be one-sided, but, if both dogs are wrestling, they take turns pinning eachother and they both come back for more after breaks, and it is ok with the other dog's person, it is usually fine with me. 
 
There are 2 huskies and a wire haired pointing griffen that Wesley (lab x border collie) lays with regularly that like to grab eachothers scruffs and necks and bite playfully.  They wrestle and growl (often all of them and fairly loudly) and do a lot of bitey face.  They also knock eachother over and pounce and then run off to be chased.  These dogs are all pretty rough and tumble.  There is often a dog on the ground, they make plenty of noise, chew on eachothers ears and scruffs and nip eachothers tails in a chase.  They are all roughly the same size (the girffen is a little bigger) and they take turns being the "aggressor" in the game and they tend to go for a while, rest - by some unspoken agreement, and then all go back for more.  All of these particular owners are comfortable with  this and none of the dogs has ever been hurt during this type of play (other than the occasional aciddental scratch).  When it gets crazy, we each call our dog to calm them down for a minute - then they will usually all go off and do their own thing for a while or start back up again/...   

Conrad can play very rough if he hooks up with another dog who also likes it rough. I keep an eye on body language. If tails are wagging and if the "top dog" position is fluid and they take turns, I don't step in. If it seems like one or the other is always beating the other up and the other is showing body language of either fear or aggression, I recall Conrad and let things settle.
 
Marlowe yells a lot when playing. He's a vocal dog just in general and his "play growl" could shake the walls. His real "step off" growl, however is quite quiet. That's how I know the difference. When playing he's all "RAWRRAWRSNORTAROOO!!!" but when really cheesed of, he just emits a low "rrrrrrrrr" that actually is so adorable I find myself wishing I had it on mp3. But adorable as it is, that's his "I mean business" growl.  I find that Conrad also has several growls. He has one that he uses just for posturing and ritualistic displays, "Oooh, look at me I am so scary!" That's the one he whips out when he thinks he's protecting me or the house. And then he has a much quieter and softer, "You'd best get lost before I eat you." that he uses when Marlowe gets too close to his stuff.

You seem to know exactly what your dog is doing but I think its just as important to know how the other dog is responding to it.  If the dog is trying to get away or not responding/encouraging your dog's play gestures then its too much (there are differences between a dog evading out of play or out of fear).  You need to watch both dog's body language but I tend to watch how the other dog is responding more than what Dodger is doing. 
So what is appropriate?  It changes with the personalities and play styles of each dog IMO.  Humping, pinning/rolling and unbridled nips/bites are generally not acceptable behaviours - but it can be fuzzy.  Some dogs accept these behaviours without being intimidated others do not tolerate them. I mostly let the dog's figure things out until I see a dog that is no longer comfortable with the interaction.  I personally find that interfering too much with dogs "at play" or interrupting necessary posturing can do more damage or cause things to get out of hand quickly. 

Dogs sometimes play rough.  If you aren't sure your dog's playmate likes it, try removing your dog a few feet away.  If the playmate comes back, all is usually well.  If not, redirect your dog to someone who likes his play style.
In general, wrestling is ok, pinning a dog to the floor so it can't get up, even if it wants to, is not.  Parallel running is fine, body slamming is not.  Mouthing is fine, and you will know it's only mouthing because the dogs' mouths are open and their tongues are relaxed and lolling out.  Biting is not.  Obsessing on another dog who is continually trying to get away is not ok - chase games look happy, a tormented dog has a different expression.  Puppy hazing or packiness (scapegoating) is not ok. In play groups, avoid the use of food or soft toys.  They tend to create tiffs.  Use rope tugs or tennis balls instead, but remove them if anyone gets too "guardy".  If dogs "go vertical" it isn't a good sign.  But don't assume that all growliness is bad.  Pit Bull pups and Bulldogs can be vocal while playing, as can many other breeds.
Brenda Aloff's book on canine body language is a great reference for anyone who wants to know more about what to look for.

When Jill was very young, she was ridiculously goofy and did not seem to understand that sometime she hurt when she played. Not at all helped by my little brother's refusal to teach his dog manners. Anyway, one day she hurt Pyry quite badly by playing too rough. She jumped on his back, and being bigger than Pyry, hurt him considerably. It was a trip to the vet.

That happened too fast and with no warning, so no one had a chance to step in and stop it. I just thought I'd share it so people might watch their bigger dogs carefully when they play with little dogs.

Rory plays different with different dogs. She has a chow friend and ALl they do is body slam eachother, its really strange. She'll even try to trip him up so he falls.
The aussie she plays with has taught Rory to nip heels but Rory only does it with the aussie.
The doberman she's plays with she is the chasee when usually she is the chaser
and my sisiter's pit she plays extremely loud with, he is the dog that sh ehas known since she was a pup and man they sound liek thy'd rip eachother to part, teeth showing growling like you couldnt believe! Taht is until you see their body language, ha ha tails wagging and just having a good time. They PLAY nicer they are just very vocal about it.
 
Ways I can tell its not nice play is by nowing my dog and reading her signs
 
-If they are excited yipping barsk
-Her tail position
-The greeting says a lot, she greets every dog with a puppy bow, butt sniff, or something of that nature BUT one time my friend and I met at the park to let the dogs play and they had never met. He was a 7 year old balck lab and when she walked up to him he didnt make a move to sniff, lick or anything which Rory noticed so she stood real tall, tail stiff and they both beefed up and were staring at eachother. We immediatly leashed them again because it didnt look liek it wqas going to go to well
 
 

[ quote]    Mouthing is fine, and you will know it's only mouthing because the dogs' mouths are open and their tongues are relaxed and lolling out.  Biting is not



Xerxes loves to wrestle and will wrestle at my feet and use my legs as barriers, or whatever.  I've been the recipient of a "mouthy" bite.  These bites are so inhibited that it is amazing to think about.  I've had my calves grabbed and quickly released (I don't taste like golden retriever) my shins bit (again I don't tasted like pharaoh hound) and everything else that can be grabbed or mouthed has been.  No pain, no marks...just double surprise.

Xerxes also loves to get beaten up by his friends.  I've watched him get body slammed time and time again...what does he do?  Puts himself into a position for it to happen again.  Never a growl, or a snarl.  But when he plays...you'd swear by all the teeth you see that he's going to kill Eva or Gus or Gaia.  But there's never any .

You'll find that puppies generally play rougher than older dogs.  My puppy wrestles, nips, paws, etc. like crazy when playing with other puppies, and the other puppies generally do it right back.  Sometimes when she tries this with older dogs, though, the older dogs issue a swift correction and walk away.  Puppies will often ut shows of dominance into their play, as well, so you might see things like humping or minor scuffles over toys or bones.  When Scout plays with puppies, I generally stay out of it unless the tails stop wagging and the growls become more snarly, which is very rare.  With SOME older dogs, particularly my BF's parent's dog, I'll step in sooner if I see that the older dog really doesn't want to play and is starting to become aggressive (i.e. genuinely pissed off at the obnoxious puppy).