Right, long post coming up (and a bit of spoiler too, so if you haven't got 100% on your Island license then I suggest skip this post).
I downloaded the Island on Friday and set out to complete the offline part. First thing I noticed was the menu colours are much better than I thought, the orange is lighter than the previous one and the blue accenting softens it a bit (I hope Criterion would release a patch that allows us to change themes though, but I doubt it). Offline didn't took me long (around 4 hours or so) and then I proceeded to do the online challenges. There's only 10 of them so with the help of a friend I knocked them off pretty easily. For the price you pay, I think the Island is definitely the best bang-for-your-buck DLC so far. It might not add much to gameplay hours, but in terms of content and enjoyment it's the best IMO. The new jumps and parking towers (especially the Big Ski Jump, Paradise Keys Jump and Inspiral Tower) just puts a smile on my face everytime.
Surprisingly, I didn't took that long to find all collectibles. I thought the Island is going to have lots of hidden smashes and hard-to-reach billboards, but it's actually pretty straightforward. I don't know if it's just luck, but I remember having much more trouble finding all collectibles on the mainland. Criterion also seems to have lowered the difficulties of events. I crashed close to 10 times

in one race and still won by quite a large margin (using the Dust Storm). I also won the Stunt Runs quite easily despite the target score being over 1 million (and I'm a horrible at Stunt Runs). The only one I found difficult is Road Rages, but that's because I couldn't get to the I-88

.
For the 9 new cars, people have mixed opinions on this one. I did some exploring on Burnout Wiki (thanks for the link Super_Spig, it's a great site 👍), and most of the people in the forums feel disappointed that they're recycled cars. I personally couldn't be happier. The Dust Storms are great stunt cars (great sound too), Toy Legendaries are just epic, and the Street Rod is much better than I thought. The Olympus is meh, but you can't have everything I guess. And the final car is just....amazing, that's all I could say (you'll have to discover it yourself once you get 500/500

). I'm a bit annoyed that they didn't make an offline version of the Rai-Jin, but I can live with it.
So I'm done with Burnout. And since this is the final DLC I can finally rest a bit (from gaming that is, schoolwork is piling up

). I'll be mostly helping out with online challenges from now on, so if any of you see me online, feel free to send an invite 👍.