OS MAVERICKS - WHY?

Apple Mac Book Pro seems OK using OS 10.8.5.

But I keep getting messages about "upgrading" to OS X Mavericks "with more than 200 new features".

I do not want any new features - I would be content to see the existing features made to work properly [ e.g. iPhoto ].

Bearing in mind the continued criticism of Mavericks, is there any real reason to install it?

I have no need or desire to be "first on my block".

I have no criticisms of Mavericks (and the iApps are all optional)

Same here, the OS works fine.
You don't have to upgrade but since it's free I see no reason not too.
There will be a time, a bit away I expect when some apps will require Mavericks but as I say that may be a while.

Mavericks works fine on my MBP and iMac. If anything the MBP is faster and has better battery life.

I have kept my MBA and another iMac on 10.8.5 but may consider updating to Mavericks at some future point.

I have not noted any 'criticism' of Mavericks but maybe I'm not looking in the right places.

Never liked iPhoto and use Photoshop for all my image manipulation.

My only criticism of Mavericks is that Apple make it (more or less) compulsory to use iCloud if you want stuff - primarily calendar & contacts - synced with your iPhone/iPad etc.

Now when it works it's fine but when it goes adrift it does so big time as I discovered when I got a desktop calendar with everything duped and an iPhone with zero entries. Fortunately I'd got loads of backups just in case.

Lots of swearing and emails but eventually I did get it sorted. However I'm very wary of the whole system and don't really trust it.

Synology NAS do come with calDAV so you could sync calendars at home using one, although AFAIK neither they nor QNAP supply anything like cardDAV that will sync contacts.

It's about six months old now and there hasn't been much criticism at all, as far as I'm aware. I can't think of a reason not to upgrade but you won't need to upgrade until they stop supporting 10.8.