Wife and I have done mixology, martini, wine, champagne, and whisk(e)y tastings. We actually owned a bar for about 3 years so it was just for fun rather than with the expectation that we would learn a whole lot of new stuff. We really enjoyed them all and would do them again. We'll probably try another one or two on our next cruise. A couple of general comments/opinions:
1. The selections are usually run-of-the-mill stuff, but a good sampling of varieties. If you are a connoisseur then odds are pretty good you've probably tried most of it before. If not, then you will get a good introduction I would say.
2. As a couple of people have mentioned, be aware of your tolerance level. They were pretty generous with the pours and that many drinks in a short period of time can be a lot if you aren't used to it. Also, not all tastings are created equal. The alcohol content can be substantially different depending on what you are drinking. We did two in the same day once and by the end of the second I was feeling it pretty good, and I generally have an above average tolerance. Nothing to be overly concerned about, but just keep it in mind and plan accordingly.
One sort of funny story about the martini tasting. My wife really wanted to go the martini tasting last minute because she likes VODKA martinis and thought they would probably be mostly that since that seems to be the trend at the moment. I'm not a huge fan of martinis in general and I REALLY don't care for Gin, but I agreed because wife. First thing out of the box they give us a big old classic Gin martini. Being the trooper that I am, I held my breathe and slammed that sucker back in a second to get it over with. The bartender took this as a sign of enthusiasm and promptly refilled me when I wasn't looking. I didn't want to be rude so I smiled and slammed that one two. From that point on she gave me an extra large pour of everything despite my politely trying to assure her that I was fine with the normal amount. I've never had so much Gin in my life.
TL;DR version:
They are great. Do it, but don't drive any farm vehicles immediately after.