My wife and I just completed a 12-night Baltic cruise on the Marina. Our previous cruise was a 12-night Med cruise in the summer several years ago on the Celebrity Solstice.
I honestly have to say that the experience was as about the same for both cruises. That is, until you compare prices. The Med cruise was about $2500 pp. This one was over $7000 pp. So, the price performance ratio was WAY out of whack.
For this cruise, we were on the Concierge level, but didn't really see any substantial difference between what we just experience from what we had on the Med cruise. For this cruise, we had some friends on a lower level and, after comparing our room to theirs, didn't really see any difference, except for a few better toiletries.