People keep recommending crappy mods for bots like Improved Bots. Honestly, I feel sorry for them that they are still unaware that this mod exists. This mod is the best thing for bots, literally, you can play through the game on Expert Realism without batting an eyelid, the bots will do it all for you. This is what you need to get through the game without having to rely on a group of people to play with.
Do you plan to develop it for L4D1? That would be great, as there is no mod there to improve the bots, I imagine for technical reasons you won't be able to (even with the 4GB memory usage patch for the game?).
You've done a very good job, I hope this becomes more popular in time, so they would stop using those alternative junk that make the bots only 1% less useless.
The best mod for the bots
This review was posted before the latest release.