If you have the chance to see this painting you should, no website can do it justice (although this is a very nice try).
Guernica is one of the few that did. Perhaps because it's massive compared to other well known paintings.
So, I just want to say, I second your recommendation for seeing it in person.
One thing I have not seen discussed here is the fact that this painting was commissioned by the (Spanish) Republican government. Effectively, there is a degree of propaganda to the painting. No shade on the guy… my other favorite war crime painting is the executions of the third of may by Goya, and it was also a political commission.
A few weeks ago I was vacationing in the Basque country, and realized Guernica (the town) was a mere half hour drive away. So we went. Although none of the town in any way reminds you of the depictions of the painting (save for some memorials), I kept feeling the same eerie dread even as I walked through a perfectly normal, pleasant sleepy town.
That early, before the tour groups have made it that far into the museum, you can actually get the entire space to yourself for >30 minutes and it's never left me not weeping.
I was similarly stunned by one of the Anselm Kiefers at the Bilbao Guggenheim. Some paintings can only be appreciated in person.