david, invasion is not "shooting hordes of stupids monsters"
it's a rush mod, solo or with other player, and survivor mod. kill a bot is easy, ok, but rush the base without dying is realy not reasy.
if you think it's so easy, try with 12 aliens, on the layout invasion-xtrem1 on atcs :p
(it's also an add-on for tremulous server)
he asked for single player, it's 2 single player mod (and multiplayer mod too)
That's one way to make people think trem is shit.
like i said, it's 2 MODS, so he will maybe think these mods are shit if he don't like them, but no trem is shit

edit : if you want train, the Wrath Newbie Training Server can help you i think ^^