Originally Posted by DArtagnan
I'm sorry, but I don't follow that logic at all.
For a lot of people, having a multiplayer mode is essential for our enjoyment of the game - as it is in my case and the case of several of my friends.
You might as well say that having no character customization isn't a bad thing, or that having no powers (ala Dungeon Siege) is just a design choice. It's not a bad thing if you don't find it adds much to the game, but if you do it's quite bad.
The whole thing is about expectations, which is why the only logic I would go along with, was if the genre standard was singleplayer only, in which case there's really no reason to expect it. However, action RPGs are pretty much associated with cooperative multiplayer - as it was introduced with Diablo (or arguably, Gauntlet) and having - at MINIMUM - the same feature set is something not unreasonable to expect of a modern Diablo clone.
In short, having no multiplayer in a modern action RPG is a negative.