Malta "must see" list opinions please!

Valetta is so compact (and enclosed by walls), I don't think getting lost would be an issue as long as you can read a map (the street names will be in Maltese). You can easily cover it on foot and there is enough to do for 6-8 hours. I think the "Malta Highlights" tour is way too much of a whirlwind tour due to the side trips to Mdina and Hagar Qim which are outside of Valetta (they're easy to get to by bus, but I honestly don't think you'll have enough time for them given they close at 5pm wish anyway). If you narrow your focus a bit, you'll probably have a better quality trip. The Hypogeum was definitely a highlight for me but you need a reservation and at least 2 hours time set aside to make it work. The beauty of Malta does require getting out of Valetta and seeing some of the smaller villages and archeological sites and the separate isle of Gozo, but that doesn't really work with the timing of a cruise ship stop - so the best you can do is just limit your reach geographically (or, alternatively, you can do a hyperactive drive-by tour like the one you mentioned).

Look on the Heritage Malta website (http://heritagemalta.org) and pick what you can reasonably see in the tight timeframe you have. Allow an extra 2 hours to have a leisurely meal and/or breaks. Definitely see the Saluting Battery and St. John's Co-Cathedral, which will likely be packed (wall-to-wall packed). If you have extra time, go visit the Three Cities (accessible by bus).

That 8 hour tour sounds like a forced march. Just wander about on your own, but do a bit of research so you will know what you are seeing. Eat a pea cake, a Maltese specialty, when you stop for lunch.

Popeye Village!

https://www.tripadvisor.com/Attraction_Review-g230152-d546981-Reviews-Popeye_Village_Malta-Mellieha_Island_of_Malta.html

I agree, the itinerary is way too full. I think we might stick with Blue Grotto, Grand Master Palace (inside too!)
Popeye's Village looks amazing. never heard of it!

Ohhh, please don't pick Popeye Village over seeing an original Caravaggio painting at St. John's Co-Cathedral. Sorry, it's too cheesy (like the film) and far away from Valetta where the ship docs, and would suck up valuable time. Valetta has amazing churches, architecture, and art - plus the oldest megalithic temples in the world (but out in the outskirts, not in Valetta proper). Look at either the Bradt Guide to Malta or Lonely Planet and be selective. The Inquisitor's Palace and Grand Masters Palace are worthwhile. If I had time for one place outside Valetta (which sounds too tight for your schedule, but who knows), it would be Mdina which is really magical.

Thank you, Agnes, for advising against Popeye’s Village. See Malta, not a film set, for Pete’s sake.

I dunno, it's been many years since i visited Malta, but distances are small, It seems doable over eight hours, and i am slow.
I found the neolithic temples by far the most compelling sight in Malta. I unfortunately missed the Hypogeum (due to poor planning on my part). The temples don't take long to see, and they are located on the sea so really beautiful. If you skip the boat trip (probably not ideal for March anyway), I don't see a lot of time pressures.