It is. But it's a mobile phone camera!! What are people expecting? It shoots great shots for the majority of people. And it's SUPER handy. This is the big selling point. Phone and camera in one and it's good quality... good enough for the average user.
I'd say they've done a great job on improving the camera.
1. Indeed it's good to have significantly better IQ (which the 5s, at least according to Apple's shots, does have), no question.
2. however, now that OIS is starting to be common with other flagships (LG G2, HTC One, 92x, 1020), it's perfectly understandable photo enthusiast do want it to be implemented in Apple's flagship too. It makes taking decent photos in hostile (almost total lack of light) circumstances much-much easier. With current OIS implementations, for example, with the 92x and the 1020, you can take 1/2s handheld shots and it most probably will be blur-free. With a non-OIS smartphone? No way! You'll be happy if you find one(!) blur-free keeper in a hundred shots...
----------
"Camera is still low quality"?
Nope. It indeed has significantly better IQ under good lighting, at least according to Apple's own press shots. I've checked them out, 1:1 zoomed in, and found them great for a smartphone.
It's the additional, essential features / capabilities like OIS that are present in other flagships and painfully missing from the 5S that disappoint a lot of power users like me.
----------
Optical image stabilisationI can honestly say I don't know. I'd have to compare different phones in practice.
As I've explained above, with a decent OIS, you can easily take 1/2s handheld shots in very low light. Without OIS, it's almost impossible - you MUST use a tripod or some kind of a stand.