Opening above ground pool that looks like a pond

We have never begun the pool season with a pool that looks this bad. Due to unfortunate circumstances, we were not able to cover the pool last fall. While I've been working for two days to remove all debris, I'm a little hesitant to just start shocking as I usually do. I have filled up with water and been running the filter for about 24 hours. The water is brownish green, has visible algae growth on the sides, and I can only see about 3 inches below the surface. Any suggestions with where to begin? Many thanks!

Shocking is exactly what you'll need to do. It's going to take a lot of bleach, brushing, persistence, and time to clear it up. If you don't have a Taylor K-2006 test kit, order one now.
Reference Ben's Best Guess Chart to find shock level for your CYA level.
The recipe for clearing a swamp is:
Raise the FC to shock level and keep it there - test and dose as many time a day as you can (at least two).
Run the filter 24/7 - cleaning as needed (when the pressure goes up 6-10 psi for a sand filter).
Brush the walls and floor of the pool at least daily - it allows the chlorine access to the algae to kill it.
Continue the above steps until one full day after:
The pool is clear, and Loses less than 1 ppm FC between sunset and sunrise, and CC is 0 (within one drop with the FAS-DPD test).
Good Luck - you can do it, I did. I opened to a swamp this year after last year's hurry-up - Sandy's coming closing.