Base game is very fun to play either alone or with friends assuming you make a friends-only lobby. Unfortunately, Valve has decided to not fix any more of the security vulnerabilities for this game as of late as they consider DDoS attacks to be "out of scope". For this reason, you should expect to occasionally get DDoSed if you or another player happen to be on the list.

Additionally, hit registration on 30-tick servers are very inconsistent since pose parameters are not lag compensated[forums.alliedmods.net], and the default command variables are outdated for modern operating systems. Of course, this can be alleviated on single-player or local servers by installing the Admin System from the Steam Workshop and adding the following command variables to `cvars.txt` in `/Left 4 Dead 2/left4dead2/ems/admin system/`:

// Hit Registration Optimizations
cl_clockdrift_max_ms 0
cl_interp 0
cl_interp_ratio 0.000001
cl_smooth 0
net_maxcleartime 0.000001
sv_client_min_interp_ratio -1
sv_clockcorrection_msecs 0