I enjoyed the singleplayer, but there are WAY better games than JK2 when it comes to singleplayer... Look at Deus Ex, Half-Life etc... But also on SP it definately belongs to the top!
On MP... Well... I didn't have much fun like this since Counter-Strike! Duels are really addicting! So on MP, it scores very very high!
In summation, JK2 belons to the best games ever, combining both a good SP and MP experience... Deus Ex was fun to play offline, but online it was soooooo terrible! Counter-Strike is MP only, with bots it isn't playable (neither can you play it with cheaters, but that's another story)...
I voted for the first option