We did our first on earlier this year, departed from Southampton which was so easy it's unreal, give them the keys to your car they take your cases park your car and by the time you get to your room cases are there!
We took in 2 stops in northern Spain, Porto and Lisbon (overnight) in Portugal and Guernsey on the return
All in all was a fantastic experience, went with p and o, couldn't fault them really had a balcony cabin (highly recommend) and went for the earlier sitting at dinner as then as said above you could get to all the shows
Entertainment on board was great and the dining, both food and service was superb.
Never did any organised trips ashore instead did our own thing and again it was great.
We were both a bit apprehensive as although we have travelled the world had never been on a cruise and in all honesty it had never really appealed, the outcome .................. Can't wait to go again
Do it properly, be selective where you wanna go and you will love it
Cruising into Porto on a sunny morning with hardly anyone about is a sight I will never forget
Hope the above helps in your decision