My wife of 16 yrs is from there so I've been there a bit. I dont think it's bad at all. But you've got to be on your toes, a bit always, but more in some areas. I've gone all over there and never had a problem. I've seen problems (muggings) though. I'm bigger than most and look in shape. Costa Ricans are small. The bad ones are looking for easier marks. I bring my family, wife and two kids there now. There's lots of interesting things to try there. Probably what I'd do is just stay at some inexpensive hotels or cabins in mountainous areas, then go on day hikes from there. Most of their national parks are the size of city parks, they're good for a few hours. On the other hand, their roads are like hiking trails, so just walking around country roads is like hiking, and a lot of wildlife are just out anywhere. I'd go alone, because I think tourist groups suck and ruin the experience, and most tours are a rip-off (meaning you really don't need to pay some overly talkative guy to go on vacation with you, and it isn't that dangerous that you need that. The times I went there alone I always meet plenty of Americans or Europeans traveling that I could have joined had I wanted to. There's a lot of tourist in Costa Rica, it's not like Iran or something, and they like Americans. Heck, there's hundreds (or thousands) of US grad students living there all the time, studying butterflies and things.
Protect your stuff and let people around you know that you are watching out for yourself. There's a lot of petty theft in populated areas, so watch your junk. Don't carry all your cash in one basket. We always get a credit card advance (of cash) one or twice each trip to avoid losing too much cash, and keep our credits card in a safe place. I'ts not really that bad there. Here's some pics of our last trip there 3 yrs ago. These are of my in-laws place near the Arenal volcano:
This shows my mini-griptillian with some mamonchinos (rambutan, fruit) and some other typical food.
Here's a pic of a Costa Rican (Corneta) brand machete that I sharpened up with a LAnskey extra course diamond hone. I later joined some neighbors clean brush from a road with it, as well as opened many "cocos", coconuts for drinking. I recommend buying a machete and matching handmade leather sheath (like the one in the pic, first thing, that way you'll have something to protect yourself with as well as something to open coconuts with. Coconuts are everywhere, and have a lot of good liquid in them but are real hard to open without a machete. You can bring it back too. Mine here cost not more than $25 with sheath. They don't come sharpened though. You can probably pay for that there though, cheap enough, or bring your own file or sharpening gear. I like to carry my machete on all hikes.
Here's a pic of my in-laws dog sleeping on a sack of coconuts that they collected for me to play with. Along side is a bucket of collected plantains, more coconuts, and a red sweetpepper bush behind.
I recommend going there. I drink tap water there and eat whatever I want, without a problem ever. I don't buy bottled water. The food and water are sanitary there.