Knights & Merchants is pretty 2D isometric RTS with action taken place in pseudo medieval central Europe. Story isn't originall; it tells about conflict of king Charle's with his son. You are king's best general and must save kingdom from rebellion.
Gameplay is similar to others old medieval kingdom sims; Settlers, Cultures 2 etc. Games has a tutorial but you can only build village in it so first few missions in campaign are quite easy and let you get used to using troops and tactics. Bulding and training is easy also. Of course later missions will be much harder and often take few hours to win.
Graphic is old fashion 2D isometric (Which I like most), very detailed and good made-up. When you build any building you will see wodden frame first to appear, next it's completed by brick walls. Units speed mapping is quite realistic, horsemen is faster than troop but when you all moving them at once they mach speed to others.
Unit sounds after longer period of time start to be little boring but for opposite music is great, with many songs tuned for particular events.
I realize that opinion about game depends of you personal taste but for me game is worth buying. You can finish it few times and still wanted more. As I did...
I don't remeber any bad game released by TopWare, all of them were good.