Having just returned from a week in Side, I thought I'd try and give a nut-shell impression of the area (without the specifics of my hotel, excursions etc)
One quick note - you do not get haggled (at all). This is WEIRD but welcome, partcularly with female visitors (just my impressions and what people told me)
The area is one of great beauty and unquestionably one of gerat historic architectural significance, so if that's your sort of thing you'll be spoilt.
You are close to many excursion activities (rafting/horse-riding/water-park etc) so you will be unlucky to spend more than an hour reaching an excursion point
Outside Antik Side (Old Town - Tourist hub) the area sprawls rather uncontrollably, with small bar/restaurant communities springing up wherever an apartment/hotel block has been built - this makes it difficult to get a real grasp on where you are, and what areas you want to be spending your time in. If, like us, for example, you are in Kemer, you may feel slightly out of the action.
The beach area is lovely, with a long promenade between the old-town and the beach. The water is very warm indeed and the beach is littered with hotels/bars/sunbeds so you'll be loked after - also each area has a shower WC etc. Be sure to have clarity on whether you have to pay for your sunbed. Even buying a couple of beers from beach waiters will not guarantee someone doesn't come up to you asking for money - the looks on their faces when you simply say "NO" is priceless. I recommend Golden Star for hassle-free/buy the occasional drink beach comfort.
The area, in general, is more expensive than other places in Turkey, particularly Gumbet/Bodrum. Although generally cheaper than the UK, I would say it is 40% dearer that other Turkish resorts 0 this leads me on to my next point - clientelle
There are not a great deal of UK visitors (relatively) to Side; main tourist groups include Germans, Scandanavians, Baltic Nations. Whilst this is a welcome relief in many respects, it must be noted that in the same way bars/pubs in Gumbet etc are all about enticing UK tourists, the same applies here to other nations. Also, although you are unlikely to see a group of Football-shirt-clad English 20-somethings chanting at local passers-by and drinking eachother's urine, you will be queue-barged, find every sunbed reserved for a week by a pair of speedos, and have people literally smoking in your face and flicking ash at you as you eat your meal.
All in all, Side is quite a sleepy town; yes you can eat and drink at 4am, but you'll be the only ones doing it - there is little to do but drink in the evening, however one plus-side is the relaxes attitude to evening/late-night swimming. No one is going to ask you to get out the sea at 3am if you fancy a dip (in fact you may get a few cheers, especially if in your birthday suit). One thing that is clear however is that during all hours there are a lot of romantic episodes going on in the sea, so think twice about wearing a mask and keep your mouth closed.