I am only 15 so this review will be from my perspective and this may or may not help you when deciding to book a cruise if you have teenage children.
I had been on two cruises before this one however they were both Caribbean. I was slightly concerned that the sea would be rough on the Mediterranean ones, but to my delight it wasn't rocky at all. The only night i felt anything was on the first night and i put this down to the fact i was getting used to it.
The Grandeur is one of the older ships in the Royal Caribbean fleet and therefore doesn't have as many facilities as the newer ships but to be honest i don't think i would've has time to use them anyway. There is a teenage club for ages 12 to 17 in which they split into two groups, 12-14 and 15-17. I am 15 so i was just in the eldest group. I thought the activities would be quite lame but they weren't. The entertainers mostly leave it up to you what you want to do and they just sit there and chat with you. I found myself making lots of friends and sitting in the Jacuzzi until 1am! My mum never saw me which to be honest i think was good.
Considering we chose an inside cabin because my mum doesn't actually like looking at the sea when there is no land in sight the cabin was lovely. Of course it is going to be a bit on the small side but in truth your never in it anyway because there's too much to do!