Online play is similar to play against bots, except that the names are different, and the tacticts change sometimes. LAN play is an entirly different game. The other night at a LAN party, I own in Quake 3. I had 4 more kills than most others, 6 being gauntlet kills. Had I done that online, who cares, I can yell a taunt at the guys online, and they can't yell back when they shove a rocket down my thoat and put me back in my place.
In Counter-Strike, there is voice chat. I stopped playing almost entirly because of this. Listening is a chore, because you hear homosexual (literally) comments every 30 seconds, and everyone sounds like they are 9 years old. You can't mute it, because people actually use it to plan attacks.
If there is bickering online, all you can do is hope someone gets booted or leave. If there is bickering at a LAN, you tell them to shut up. Once I unpluged the hub because two kids were arguing over the "n00b c4|\||\|0|\| in CS. We told them to shut up or they wouldn't be playing, we re-started the server, and all was well. We even got to keep all contestants.
Internet is great when you are home sick or when everyone is busy, but there is nothing like a LAN party.