I spent two weeks in Belize & Guatemala in 2012 for the Mayan calendar change.
Belize was awesome. I spent time driving around the country, going to various ruins, & doing touristy activities - a few tours, some hiking, etc. I had wanted to go diving, but had a cold so I went snorkeling instead - it was still absolutely beautiful.
I was only on Ambergris Caye for a few hours. It is very touristy, but if you like beach vacations, I can see the appeal. I spent a few days on Caye Caulker - which is also beachy and touristy, but less so. The cities on the mainland were very different than the islands. San Ignacio was the jumping off place for a lot of the adventure tourism, and a good place to go if you’re into that kind of thing. I also spent some time in and around Orange Walk - not off the beaten path, but definitely a less traveled path than the islands. It had a very different feel than the places entirely driven by tourism. And I absolutely loved Hopkins - which is tourism adjacent. There are resorts to the south, but Hopkins itself is a small town on the beach at the end of the road. (It’s also the only place I’ve ever been where I could blend in. Well, at least until I started talking.)
I liked it. I’ve recommended it to other people and I’d go back for vacation. I’m not sure I’d live there, but it’s not an automatic “no.”