I am familiar with the Ottertail area, as my family has had a cabin on Big Pine (Perham area) for several years. I don't make it that way very often anymore but have had some fun trips out that way. You have a lot of options in that area...West Battle Lake & Big Detroit for muskies...like stated...just about every lake has largemouth. The walleye fishing does not hold a candle to SAK/OAHE/Devils Lake though, so wouldn't plan around that being the primary target. Can also get some good panfishing in...lots of the lakes have giant gills and nice crappies as well. I've enjoyed trips out that way but if you are looking for a TRIP type experience, I think I would look to the north (LOTW) or west to Fort Peck....