My best suggestion would be somewhere on the Riviera Maya (the stretch of Yucatan coast running many miles south of Cancun) or even Cancun itself.

There are abundant spa like properties where you can get your pamper on (with a wide variety of options in terms of taste, price, vibe), even more small boutique like places offering intimate surroundings and service, great snorkeling in several areas (reef off of coast of Puerto Morelos, lagoon at Yal-Ku, underwater caves, and off-the-beach snorkeling with real live sea turtles at Akumal). Plus Cozumel is close by.

Plus there are all kinds of exploration/wildlife/outdoors adventure tours available--everything from Mayan ruins (Chichen Itza, Coba, and Tulum) to wildlife excursions at Sian Kaan. And cities like Valladolid and even Merida are not that far away if you want more of a colonial vibe. Not to mention Xcaret which has everything, plus a crazy spectacle of an evening show.

It's a perfect place to have leisure one day, and then adventure/cultural activities the next.

I'd do a split between the Arenal area and Manuel Antonio in Costa Rica or maybe go to Belize and do a split between jungle and beach.

Thanks!

We loved Victoria House on Ambergris.

Belize has awesome snorkeling. Ok beaches, some shopping. Lots of active things to do, cave tubing, hiking, canoeing, kayaking, cave exploring. It's easy since English is the official language, also because it's small and easy to get around.

We went to Curacao last fall. It's a pretty island. The best beaches are on the west end of the island, so there's some driving involved. Good restaurants. I'm not a shopper, but, downtown Willemstad appeared to have lots of options.

I will second the Riviera Maya suggestion - some of the best beaches and snorkeling anywhere. Mayan ruins, great dining, cenotes, caves, etc. Very safe and inexpensive. The only down side may be that the countryside is not particularly scenic away from the beach - flat scrubby jungle with minimal hiking opportunities. Lodging options run from funky bamboo huts to huge AI resorts. Go to locogringo.com for lots of info.

Costa Rica doesn't offer good snorkeling. The best snorkeling will be in Belize but the Riviera Maya has better beaches. What kind of exploration are you interested in? Costa Rica is great for wildlife and Belize is as well, maybe to a lesser extent. Belize and the Riviera Maya have Mayan ruins. Costa Rica has volcanoes.

Not sure what you mean by the Sandals vibe of St Lucia. I enjoyed the lushness/beauty of the island but prefer whiter sand beaches.

Costa Rica isn't great for snorkeling, especially in May. But I would check out the Manuel Antonio area, it's touristy but still maintains the Costa Rica culture and has a laid back beach vibe. For a honeymoon couple I would recommend staying at Tulemar - Tulemar Vacation Homes. It's a resort community, with small bungalows and villas, four pools, hiking trails and they have a private beach that offers free lounge chairs, umbrellas, boogie boards and sea kayaks. There is a coral reef you can go to on the kayaks, but the visibility isn't great. The private beach also has a beach bar and grill. It has a good central location, it's very jungly, you have the chance to see lots of wildlife - sloths, monkeys, iguanas, birds etc.
The Manuel Antonio area has a lot of day trips you can plan, zip lines, water fall rappelling, white water rafting, ATV tours etc. Plus the National Park has some of the most beautiful beaches in the world!

I agree with Volcanogirl, the Arenal area of Costa Rica is a must see as well. You could split up your time between Arenal and Manuel Antonio. The Nayara Resort is beautiful, perfect for couples and was recently named the 6th best hotel in the world by Travel and Leisure magazine. It's also listed as one of the most romantic hotels in the world. You could visit the hot springs, and have a relaxing spa day - check out Tabacon.

If you want an adventure type honeymoon I recommend Costa Rica!