My week at Belizean Shores in January was great, and although not a romantic celebration (I traveled with my sister), some things are great no matter the occasion! I second the above suggestions for snorkeling with Alfonso, and dinner at Caliente Norte, which is a short walk from your condo. The food really is local style, although the ambience is "elegant" rather than "funky". Prices seemed reasonable to us for what was offered.
I have photos that may interest you in my "Belize 2006" Shutterfly album -- it's under the Trip Reports and Photographs section of this web site -- shots of Belizean Shores (inside & out), Caliente Norte (ditto), and snorkeling with Alfonso (in both sets of Belize photos -- January photos are named "Belize 2006", and the second set is named "Belize May 2006).
What a great place for a honeymoon!