I did it from the top with someone about 3 or 4 years ago. Total fiasco. We both broke our boats within an hour of putting on (sharp quartzite broken river bed). I personally do not believe it's worth the hike since it's 1:1 walking-to-boating and most of the river lacks definition with the underlying rock being sharp and broken. If I lived in Laramie, sure I'd probably do it once a season if that's your thing. Still think the Encampment is 10X's better and no hiking required.
If I was to do it again, which I will not, I would recommend taking a playboat (lighter) as long as you're cool with class IV creeking in a playboat. I would also definitely hike in from the bottom (is it the Arlington exit?). There's a pretty major confluence about 6-ish miles up from the trailhead and this is also where the hardest rapid was. Everything above that was easy peasy on the main branch, so I'd recommend putting in no higher. After the confluence, there was one rapid (the confluence one at the very start) that seemed like IV+ and the rest was III-IV boogie, mostly III.
Just for humor, here's the story. So my buddy and I drug in from the Centennial side after getting shut down from the north (up the pass we took some road that went north towards I-80). Of course eventually we hit snowdrifts and started dragging. Unfortunately, I kept dragging after the snow stopped drifting. By the time I got to the put-in my boat had a dime size hole in the bottom. Lesson learned #1 - don't drag your boat on gravel. No bich, so we did as best we could with duct tape. Lesson #2 - bring bich for hike-in runs. There was no going back because the shuttle folks had already started hiking back an hour earlier. Damn. So we put on and the duct tape held for about 5 minutes. After that its efficacy went from 90% to 0% in about 45 minutes. Since the water was easy and I had a dry suit I'd just go as long as I could then drain it and do it again. My buddy Brian was laughing until, oh, maybe an hour in, he hits a rock in his Gus and sends a 10 inch crack across his bottom. Then he's leaking worse than me and he's only got shorts for the snowmelt water in his boat. So we both start riding swamped boats down the unknown creek. The good news was that with all the wood, you had to get out and drain a lot anyway. The bad news is that with all the wood and a swamped boat, every corner was filled with apprehension. Course you had to trade downstream progress before dark with the thrill of possibly rounding a corner into a strainer...nice. Anyway, we got to the confluence I mentioned above and there's the best rapid, but at this point, maybe four miles in, the holes in our boats are so big that you can really only ferry to the other side of the river before there was too much water in the boat to navigate it safely. It was getting late so we left the boats and walked out. Our shuttle friends on the other end were very happy to see us.
I joked that we should have just left the boats swinging off ropes from a high branch above that confluence rapid as omens to future kayakers, but of course that's littering and it wouldn't be cool. So, as if one weekend wasn't enough, we came back again two weeks later and drug them out. By the time we got to the parking lot, the hole in the bottom of my boat was big enough to poke my head through. It was also sweet walking 6 miles of runnable river twice because we broke our boats before we even got to it. Anway, that's my memory of Rock Creek from the top in the Snowy's. It's like a class 3-easy 4 version of the Encampment, but with hike-in access. I believe the level when we were there was maybe 600 cfs at the takeout gauge and it was probably sometime in June 2006. The NF of the Laramie or maybe it's the Little Laramie??? also had some cool looking IV-V boating, but it was short and snow made access difficult for that, too.
Here's a few pics from our debacle.
Damn it feels good