Depending on how full the day use area is, you can literally drive to the waters edge and park 20 feet from the water. There are picnic tables along the lake shore as well as a single washroom.
We were there on two different days and faced smoke both time. The pictures on the web of clear days are amazing, with a lovely green lake and amazing mountains in the background.
It was lovely all day when we were then.
Immediately beyond the dam is Lake Minnewanka proper. Minnewanka is a pretty huge lake that can really roll in the right wind (or really any wind). Two Jack offers a very similar experience with much calmer waters (although a big blow can be pretty rough).
Overall, this is a lake we'd go back to on a sunnier day. Truly lovely clear water, interesting bottom and shore line and lots of see.