Hi rugnuts, Lucky for me that I'm in 'northern' Minnesota when it comes to the trails.
If you're ever up in the area, I really enjoy the 'Thistledew' trail for a long relaxing trail ride. There are several nice lakes to see, picnic areas, some shelters with fire rings and a nice parking area. Not much for technical challenges but it's an enjoyable place to ride.
If you're up on the North Shore the Red Dot/Moose Run trail is fun. There are lots of terrain changes, some mud and lots of red goo (you're on the Iron Range) to drive through. You get to see some of the North Shore and lots of old mining areas along with plenty of tall pines. The trip up to Finland is a blast. A little more technical in places.
Round River trails are strewn with narrow sections and a fair amount of fallen trees after windy days but it's a fun ride if you like lots of twists and turns. Lots of elevation changes and there's a nice bar & grill near the trails for lunch or dinner. I've been down there many times and enjoy it more every time.
Moose River is great but what makes it even greater are the trails that attach to it by the efforts of the Over The Hills Gang ATV club. They've worked extremely hard to build and maintain a full network of trails for everyone to enjoy. They've published excellent maps and the members are very proactive in the care, maintenance and control of the trails so that a few idiots don't ruin it for the bulk of the users. You can ride the Moose River trails and then travel down to Outing & Emily, MN for lunch and fuel. There are over 100 miles of combined trails and it's one place you have to try.
Red Top has a little more of a technical side (in places) but it's not tough to ride. I've only been there once but it would be fun to go back for another ride sometime, I really enjoyed the elevation changes and the interesting forest areas.
That's my synopsis of a few 'northern' trails. I'd still like to get over to Spider Lake, Blind Lake (near Aitkin) and the new '70-mile' trail opening up this summer.