My girlfriend and I did this tour as part of a 4 in 1 tour booked through www.arenal.net
I think most people visit La Fortuna to see the volcano, so going on this tour is a no brainer.
We had a guide and a group of 8 tourists and this tour took a couple of hours.
We were taken to the side of the volcano opposite to most of the hotels, which is the current "active lava flow" direction. In the parking area, you are at least a couple of kilometers away from the base but this is as close as you are able to go. The conditions for seeing the volcano were decent. There were no clouds, but the volcano was constantly smoking and this can obscure the view of the peak depending on the wind. Anyway, we walked a short ways around the base (from a distance).
It is very nice having a guide to tell you about previous eruptions, show you some interesting plants, spot some birds etc because contrary to popular belief, the volcano is not constantly spewing lava. In fact, it is very rare to see any glowing lava at this volcano.
While we were walking along, there was a loud rumble and a small eruption, consisting of some steaming massive rocks getting tossed down the side of the volcano. I think that's about as much as you can hope to experience.
It's a worthwhile tour and an appropriate length of time. Kids could tolerate it.





