Over the past 8 winters I have spent allot of time in LaFortuna. It is a small, tourist town with wall to wall tourist agencies and gift shops. Generally it is safe to walk the main street well into the late evening. There are a couple of annoying things about the town. One is traffic noise which can be excessive, mainly because a few young guys with motorcycles and ATVs that are withouit proper mufflers, etc. The second thing is that it is the short-change capital of the world. Even the clerks in the supermarkets will short change you by a few 100 colonies if you look like a tourist. If you deal in American dollars, you are even more likely to end up a few dollars short.
The main attraction that has drawn tourists to this little town has been The Arenal Volcano. It is a huge imposing land mark at one end of the town. On a clear day, it affords a super photo Op - especially since you can line the church and the park up with a view of the volcano. Unfortunately Burger King as seen fit to move into a spot so that it's sign is now plastered against the volcano in many shots. But that can be clones out with almost any photoshop program.
The other unfortunate thing is that Arenal has been sleeping for over a year. Until 2011, it was possible to take a night tour around to the active side and watch the natural fireworks. I was there once when there was also an impressive thunder and lightening storm in progress. Magnificent!
There are many other tours though and lots to do and see in the area. I would suggest that you go from agent to agent before booking a tour. Many will give you discounts, especially if you book more than one tour with them. The same applies to buying gifts. An item that is $15 on one end of town is often $10 on the other. There are lots of nice places to eat; hotels run the whole scale from backpackers to elaborate. Bus and transfer service to and from is excellent.