They've given hints there will be another (or another similar game). Mainly by saying on their facebook page not along ago that "evil always finds away" and it sounds like they'll be using the Unreal Engine 4 for it based on the hints.
http://www.eurogamer.net/articles/2013-02-07-triumph-has-been-working-on-a-new-overlord-experienceI too thought the first was better but only because of the customization aspects. You could enhance weapons and armour with different minions producing different effects. Overlord 2 removed that and replaced it with armour and weapons with different benefits, however they were rather minimal and the customization mainly focused on the minions instead who actually levelled up this time around and could be resurrected. I liked the world of the first Overlord more too.