GCS Single Region is pretty much directly equivalent to standard S3, and Nearline is equivalent to S3 Infrequent Access, complete with per GB retrieval fees. Storage for both classes is cheaper than the respective S3 classes. Operation fees are exactly the same though.
There's two other storage classes though:
One major feature is multi-region buckets for $0.006/GB more. Presumably built to avoid incidents like us-
tirefire-east-1 falling over and your buckets disappearing, it's a definite point if you need high availability (and are willing to trust that Google has proper HA).
Assuming single region stores 3 copies, I speculate that for the price, multi-region stores 2 copies in each region for a total of 4 copies. That (suspected) single additional copy would be why multi-region buckets are only a third more expensive.
Coldline is a bit more interesting. As the equivalent of Glacier, it has one big advantage - quick retrieval times (on the order of a second), much better than Glacier. The downside is the fixed retrieval costs - $0.05/GB. Just comparing Coldline to Nearline means you shouldn't retrieve anything more than once every 2 years(!) if you want to save money compared to Nearline. (Nearline is $0.01/GB, Coldline is $0.007/GB, so you save $0.003/GB/month going for Coldline.)
In comparison, Glacier has a number of retrieval speeds and corresponding retrieval pricing. Even Glacier's expedited requests (the most expensive option) cost 40% less than Coldline. (Interestingly, the bulk retrieval option works out to about 25% of retrieving from S3 IA, but takes in the order of 8-12 hours.)
Considering Glacier costs almost 50% less than Coldline, I really question the utility of Coldline. With the restore costs it only makes sense if you're storing archival data that doesn't need to be accessed for around 2 years. I think Glacier has a much better handle on the expected use cases here.
I can see Nearline being used (and people having the expectation of immediate access), but the retrieval price of Coldline with no way to change that makes me very leery of using it.