Excessive lactose in a milk stout?

As I understand it lactose does not get fermented by brewer's yeast and adds a distinctive sweetness and body to a beer, i.e. the milk stout style. Is there a point where lactose additions can add too much body to a beer? If so, what characteristics, sweetness aside, would one look for in a beer with excessive lactose?

So, this line of questioning all stems from last night when I drank The Bruery's 8 Maids-A-Milking, which is an imperial milk stout fermented with Belgian yeasts. I liked the flavor of this beer a lot and I think it was a unique twist on typical Belgian-style stouts. However about mid-way through the bottle the texture/mouthfeel was really bringing me down. The best way I could describe the texture was that it was slimy. A tasty sweet Belgium imperial stout slime, but slime nonetheless. It appears that most people describe 8-Maids-A-Milking mouthfeel as thick or velvety, so maybe I'm being overly negative with my descriptor, but needless to say it ruined the experience for me. But, I don't think I've ever had an imperial milk stout before, so I'm trying to confirm my suspicion that was the added lactose causing this effect on the body/mouthfeel.

 

To be fair, I don't think The Bruery made a mistake here and I'm sure 8-Maids-A-Milking is exactly as they intended it to be. The beer just wasn't for me and that's fine. In over a decade I have never felt compelled to describe a beer as slimy, so I am trying to figure out what about the beer/brewing process created this unique [to me] characteristic.