If you were a fan of the original CoD, you will most definitely enjoy this as well.

User Rating: 8.5 | Call of Duty: United Offensive PC
Good: same old fast paced and intense game play from Call of Duty 1, new weapons such as flamethrowers and silencer attachments, better cinematics and cut scenes, new vehicles such as boats and airplanes that are able to be used for gunning

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.