I refer to it a bit towards the end of this article:
http://caratacus.journalspace.com/?entryid=1050
To these points I'd add, in no particular order:
1. The main source is Tacitus, who was biased because he was a Roman but also because his father-in-law was a governor less than 20 years later. Agricola may have had (Gallic) Celtic origins, as did Classicianus, the Procurator (chief financial officer) of the province appointed after B's revolt. This probably reflects a conscious effort on the part of the imperial admin to "soften" the previously harsh Roman rule over Britannia.
2. The harsh governor at the time of B's revolt, Suetonius Paulinus, and the grasping Procurator also of that time, Decianus Catus, seem to have had contempt towards the Brits and treated them harshly. So the change noted in #1 may have been an attempt to make life easier and revolt less likely. When B's hubby Prasutagus died, Catus saw an opportunity to rip off the widow.
3. Roman money lenders (including the "noble" philosopher Seneca) had forced native British aristocrats to borrow money at high rates of interest, for such purposes as bulding the imperial cult-temple at Camulodunum. According to Cassius Dio, they suddenly recalled these loans and severely embarrassed the Brit aristos, pushing them into the revolt. The bronze head from the is temples statue of Claudius was ripped of by the rebels and flung in the River Alde -
http://www.unc.edu/celtic/catalogue/boudica/claudius.html
4. Back to Tacitus's biases. He was pushing a line that Roman society (especially under Domitian) was decadent, so liked to contrast "noble savages" with the allegedly soft and over-civilised Romans. Hence "A contrast to the servile society of Rome is the Noble Savage type. This is embodied in figures such as Calgacus, Arminius, Boudicca and Caratacus" (Type Characters in Tacitus by B. Walker). So many of the fine sentiments put into Boudicca's mouth tell us more about Roman attitudes than about Celtic thinking.
5. The previous emperor Claudius had kept a close eye on the provinces, including his own pet project Britannia. But after his death in 54 Nero had been not at all interested in provincial affairs - apart from cultural contests in Greece - and so the provincial administration had run down and was at the mercy of bumptious types like Suetonius Paulinus. The veteran colonists in Camulodunum, in the territory of the Iceni's neighbours the Trinovantes, were, for example, arrogant and prone to thieve native land and money; so they were early targets of the rebels.
6. The revolt gave the Romans a terrible shock (rather as if the US army were severely mauled and nearly defeated in Iraq ) and I think the most important result was that the Romans seem to have made a big effort to appoint sympatico officials there, such as the procurator Classicianus and, later, Agricola.
There's some good sources here:
http://www.stephen.j.murray.btinternet.co.uk/boudicca.htm