Quite different. Bariloche is in the Lake District, greener and with lakes. El Chalten is in Patagonia proper, more mountainous. I haven't finished posting the photos from my SA trip yet, but there are some on my blog:
mytimetotravel.wordpress.com

Just got back from Calafate and Chalten. Have been all over Argentina except for the lakes and Bariloche. The chocolate there is outstanding our guide said, Swiss immigrants. Along with Iguassu the Calafate (ie Pietro Moreno Glacier) and Chalten (Cerro Torre/Fitz Roy) areas are often called the don't miss areas of Argentina. It is a tough call if you have already seen and done mountains and glaciers other places. I too have trekked many mountains in many countries and new ones never get old. Maybe because it was just last week but the hike to Fitz Roy was really special, my fave out of three weeks in Patagonia. Great views all along the way and drinking out of pure glacial streams. The hiking is true mountain hiking and may be considered strenuous for some depending upon their conditioning, also the weather can change in minutes. My mt guide said the fishing in the rivers there was good. Most trails start right in the town. Chalten is a throw back trekker town, heck it didn't even exist before 1985. I can recommend the Senderios Hotel, a great B&B style hotel...lots of hostels and cabanas there also. Calafate is really the gateway of sorts to that region as the airport is there, bus terminal to Chalten and the starting point to visit the glaciers. If glaciers are of no interest just by pass Calafate, though the lake there is huge (possible fishing?). A word of advice if going to Calafate/Chalten be sure to have pesos before you arrive. Changing money was nearly impossible. Though many people take and sometimes welcome US$ the few ATMs had lines of 50ppl and the banks close early and ATM in the bus station in Chalten often runs out. As a pro photog I hope to get some images up soon and get the blog finished but editing 6000 images takes awhile. My 2cents, enjoy your trip.