Lac Blanc is a beautiful and rewarding hike! The endless views of the surrounding mountains are breathtaking we ran across an Ibex on the trail.In good weather the views across the valley to Aiguilles Verte, Les Drus, right up the Mer de Glace to the Grandes Jorasses and across to the Mont Blanc Massif and Chamonix Aiguilles are also visibale. The lake itself was very nice but a little underwhelming, extremely busy and has two restaurants which for me always takes the wind out, since it makes it feel like a tourist spot and not a hike.
Take into account the the final 15 min up to the lake are uphill and more demanding and also that the end of the trail is quite a steep path downhill and then uphill (due to an avalanche that blocked part of the path). The cable car back is very busy, especially close to the closing hours (waited 30-45 min in line).Even though it's quite high (over 2000 meters), it was very hot while the sun is out on a mid summer day. I would definitely do it again but start a little earlier and take a longer break on the lake.