If you were a fan of the original CoD, you will most definitely enjoy this as well.
Bad: somewhat cornier dialogue/characters at times during cut scenes
From my CoD1 review (also applies to United Offensive):
-smart enemy AI, many different environments, lengthy campaign, great graphics and sound effects for its time, able to use unique weapons such as flak guns, tanks, panzerschrecks, etc., pretty destructible environment for its time (glass windows break, trees fall over, etc.), different missions/tasks such as defending buildings, destroying enemy weapons, supporting your squad, flanking enemies, taking out snipers, retrieving intelligence, etc.
-sometimes hard to find out where compass is pointing to, no grenade indicator, squad AI sometimes lacks intelligence
Overall: If you were a fan of the original CoD, you will most definitely enjoy this as well.
Online: I did not play online so I cannot comment on this.