Fish Creek is located in the Southern end of the Calgary. It's a good example of what Calgary looked like before the urbanized Calgary we see today.
I was only at Fish Creek for a few hours on a Summer day as a tourist and only explored the trails near the Bow Valley Ranch visitor center. Visitor Center was closed on Sunday. The trails in this area are pretty tame, and there are plenty of bicyclists and local residents out for a walk. It's mostly flatland. Vegetation includes ponds, creeks and some scattered wooded areas. There are suburban residential areas immediately surrounding the park and a few trails lead directly into people's backyards. In the wooded area, there was a mini-trail we walked thru. Trail was completely shaded and surrounded by dense amount of trees. A cool breeze came thru and there were falling leaves all around us. It was an interesting experience.
As an international tourist, time is especially valuable. Is it worth it spending a few hrs here vs spending that same additional time in Banff or the Three Sisters area? Hindsight probably I'd go with a few more hrs in Banff. Nonetheless, if you have a extra hrs in Calgary unplanned, this is a good stop. Parking is free.