Spend enough time on various travel sites and you will come away a little confused by what Sihanoukville (or Kampong Som) has to offer. Being Cambodia's only deep water seaport makes it a busy small town but there happen to be various levels of beach destinations there which bring in western backpackers and others, many escaping the more developed commercial leaning tourist centers of Thailand's larger and more experienced vacation machine.
The town itself in the past was not much to write about. Previously a mish mash of old shacks, dubious constructed concrete blocks of buildings interspersed with homes, bars, shops, little markets, a cacophony of motor bikes and cars following who knows what traffic laws as well as a burgeoning nicer hotel trade catering to the growing gambling business that is here as well as cheap and mid level guesthouses.
Some come and find a beach to their liking, while others bristle at the constant pressure of street kids working as touts and junior merchants. Stay long enough and you will notice western men with their concubines. Their ages? In all fairness to the locals who are petite by nature unless you ask..enough said. If that doesn't cause you to go "hmmm" many people always report the level of drug touts and taxi girls around. You would have to be blind not to notice this in "certain" locations.
All of that said there are several major beaches to enjoy. Victory beach...not far from the old backpacker budget area, which with the likes of Chil-axn, Beach On The Hill BBQ, Space Cats, Whiskey Bar, Johnny Walkers and more is making a come back. It is also popular with locals,especially on the weekends. Not "upscale" by any means but a nice sunset.
Occheuteal Beach and Serendipity Beach...the most popular and tourist-ed with all the guesthouses, deck chairs, beach bars, touts, beggars, drunken jet skiers and beach fun you need. Nice sand, just busy.
Otres beach...though slated for and developing quickly, there is still enough quiet sand to get away, especially in the off/slow/rainy season. But note, the tuk-tuks won't travel the road to and from Otres at night.
Independence beach..quiet with small strips of nice sand at low tide. Being developed.
Sokha beach...a local gem. The cleanest beach around. Not much in services but quiet and calm.
Ream and Prek Treng are further and usually empty. Grab a book!
A few days of low cost sand still exists here...caveat emptor!