The game is like a cross between an RPG and a RTS. It is more a true role playing game, in that you actually play a role and it isn't as heavily abstracted as it is in standard RPGs. The combat is very similar to Oblivion, although they did a better job at combat than Bethesda. Still, the closest game I have played would be Oblivion when it comes to combat. Building armies is somewhat similar to Heroes of Might and Magic, in that you have to recruit from the cities and villages you own (or the prisoners you pick up). The city building is somewhat similar to HOMM as well, although this part is far more unique. It is probably the weakest part of the game actually, as your city/village building options are very limited.
The last time I played the game, the issues with maintaining nobles and the bugs with the noble AI annoyed me enough that I stopped playing. This is only really an issue late in the game, since it takes a long time before you are powerful enough to command a large number of fellow nobles. Also it is likely much better now, since TW was releasing patches on a nearly daily basis back then, so by now most of these issues are likely fixed.