Even if information about BigTable is scarce — basically everything known so far coming either from the original paper  or from Jeff Dean’s presentation , Lars George manages to compare over 40 features and concludes:
If HBase as on open-source project with just a handful of committers of whom most have a full-time day jobs can achieve something even remotely comparable I think this is a huge success. And looking at the 0.21 and 0.22 road map, the already small gap is going to shrink even further!
For an excellent reference to HBase architecture, I’d recommend another article authored by Lars George ☞ HBase Architecture 101 - Storage.
Now based on this HBase vs BigTable Comparison and this other one on HBase vs Cassandra, you can conduct your own three-way comparison and see if you agree that Cassandra is winning the NoSQL rage.