I remember watching the artillary bombardment on the TV when the war started, it looked very impressive, but later it appeared that all those bombardments had no effect becuause vietnamese built their bunkers mostly halfway in the hills where it can only be reached by rockets.
The casualty was very high in the beginning because of the bad commanders, by that time the PLA had been in bad shape for like 15 years, Mao's culture revolution did the same thing to PLA as what Stalin did to his red army before the 2nd world war.
However, Vietnamese knew they could never stop a chinese advance, no matter what, their best chance was to delay china in the mountainous border region, and did their best to cause chinese casualties, however, casualties was not something that china cared much at that time, a date was set to capture the strategic city Liang Shan, and Liang Shan was captured in time. From there, Vietnam lies open.
Vietnamese fought a very bitter war, they would fought to death even when completly surrounded, their villigers , from young kids till old women, often carried out suicide attacks on chinese soldiers while chinese army tried to keep them out of the battle, on one account, vietnamese special forces infiltrated the frontline, captured a chinese field millitary hospital, and killed all the docters, nurses and wounded soldiers. The last was a big shocking news to chinese soldiers, they didn't expect vietnamese soldiers to kill those defendless people in cold blood. I think from that point the wiping out of complete vietnamese villages started, no one were spared.
That was a stupid war , I think both sides now just want to forget about it.