A quick summary:
It is a five year extension of the current deal, lasting now till 2018/19 for the shirt sponsorship.
The "Emirates Stadium" name will be part of this, lasting till 2028.
Arsenal will be getting £30 million per year over the next five season.
This deal will move Arsenal to the 2nd highest shirt sponsorship deal in the Premier League, only behind ManU. (and it is a more lucrative deal than Real, Barca, Bayern etc.)
This is a huge step up from the current Emirates deal and will go a long way to keep the club self sustaining and perhaps raise some wages, or increase transfer spending (to a degree).
The only downside I see is that the Stadium name rights were part of this deal. As we saw with Man City and PSG, those naming rights can be very lucrative on their own, so including that 15 year extension in this deal seems like a discount for the Emirates. Either way it's a big boost in commercial revenue (with a new kit deal coming also).
Really gives Black Friday a new meaning!
Update: Adding some comparisons.
Manchester United's deal with GM will pay them $559m (about £347m) over 7 years. That is about £51m per season (actually less since GM will pay United over the next 2 season even while not sponsoring the shirts). United have an immense global brand so it's not surprising they have a deal this large.
City signed a £350m deal with Etihad that last's for 10 years. The breakdown is £20 for the shirt sponsorship and £15 for the Stadium naming rights(£35m total per season). Our new deal compares favorably to this, because even though ours is £5m a year less, the contract is only for 5 seasons, meaning a new, more profitable deal could be reached sooner than City.
Chelsea had their deal renewed by Samsung for around £18m each of the next 2 seasons. With no Stadium name rights, this leaves them a bit behind the other big commercial teams. Chelsea of course would be on course for a large increase in 2 years, perhaps a new stadium and naming rights to go with it.
Over all this moves us into a much more competitive commercial position in the league, and while we are behind United in this regard, we can be excited that Arsenal are getting a top market value for their sponsorships.