Well to do a proper roast imo you would need to put the potatoes in the oven.
Meat done ion the slow cooker is beautiful though, it's so tender. Sear it in a pan first then chuck in the slow cooker with a bit of stock and whatever herbs / spices /condiments you prefer. I put onions and carrots in with mine. Cook on high for 3-4 hours or low for 7-8 hours.